Changed identifiers in code to avoid standard C/C++ naming convention conflict.

Closes #11

See merge request !19

Dropped unused conflicting identifiers where possible and renamed code
identifiers from _something to something_ when the identifiers were used.
Only internal identifiers were changed, so no API/ABI change.

These were tracked down using clang -Wreserved-identifier.  Extended clang CI
check to detect such issues in the future.

Fixes #11.

This could detect issues not discovered by valgrind.

New Debian and rewritten autoconf/automake logic fixed the issue.

Since all abbreviated months are three characters followed by a NUL
byte, this buffer should be 4 bytes.

Leftover from 25431ddc.

Three implementations in tools/ were dropped and one common implementation from
oggz_byteorder.h is used instead.

<URL: https://wiki.sei.cmu.edu/confluence/display/cplusplus/DCL51-CPP.+Do+not+declare+or+define+a+reserved+identifier >
states:

  "Each name that contains a double underscore __ or begins with an underscore
  followed by an uppercase letter is reserved to the implementation for any use."

Changed all header files to avoid conflicting with this convention.

Related to #11, but there are other conflicting identifiers left.

Ran autoupdate and edited setup until most warnings disappeared.

Switched valgrind run to use LOG_COMPILER and fail on valgrind errors.

See merge request !17

This wil avoid running valgrind on bash and instead validate the
test programs themselves.

Disabled shared library building, as the linker could not find -lc.

Fetches latest Ogg library from git and build it for Windows to
have it available for Oggz.

fixed random access offsets

See merge request !10

Introduced new configure option --enable-debug to build with -DDEBUG.

See merge request xiph/liboggz!12

Bring OggzStreamContent enum in line with documented return values.

Closes #16

See merge request !13

Stop trying to read comments outside the ogg package available.

Closes #14

See merge request xiph/liboggz!11

Avoid reading invalid memory in dirac_frate_tbl.

Closes #15

See merge request xiph/liboggz!7

Avoid crash when inserting comment with no value.

Closes #13

See merge request xiph/liboggz!14

This fixes the following issue as reported by valgrind:

==2828942== Invalid read of size 1
==2828942==    at 0x4847743: __strcmp_sse42 (vg_replace_strmem.c:927)
==2828942==    by 0x485505A: oggz_comment_cmp (oggz_comments.c:219)
==2828942==    by 0x485505A: oggz_comment_cmp (oggz_comments.c:213)
==2828942==    by 0x485B243: oggz_vector_tail_insertion_sort (oggz_vector.c:237)
==2828942==    by 0x485B243: oggz_vector_insert_p (oggz_vector.c:286)
==2828942==    by 0x4855B5F: oggz_comments_decode (oggz_comments.c:664)
==2828942==    by 0x485A86D: oggz_auto_read_comments (oggz_auto.c:1510)
==2828942==    by 0x4856E43: oggz_read_sync (oggz_read.c:456)
==2828942==    by 0x485738B: oggz_read (oggz_read.c:650)
==2828942==    by 0x10AD64: validate (oggz-validate.c:445)
==2828942==    by 0x10A431: main (oggz-validate.c:594)
==2828942==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==2828942==
==2828942==
==2828942== Process terminating with default action of signal 11 (SIGSEGV)
==2828942==  Access not within mapped region at address 0x0
==2828942==    at 0x4847743: __strcmp_sse42 (vg_replace_strmem.c:927)
==2828942==    by 0x485505A: oggz_comment_cmp (oggz_comments.c:219)
==2828942==    by 0x485505A: oggz_comment_cmp (oggz_comments.c:213)
==2828942==    by 0x485B243: oggz_vector_tail_insertion_sort (oggz_vector.c:237)
==2828942==    by 0x485B243: oggz_vector_insert_p (oggz_vector.c:286)
==2828942==    by 0x4855B5F: oggz_comments_decode (oggz_comments.c:664)
==2828942==    by 0x485A86D: oggz_auto_read_comments (oggz_auto.c:1510)
==2828942==    by 0x4856E43: oggz_read_sync (oggz_read.c:456)
==2828942==    by 0x485738B: oggz_read (oggz_read.c:650)
==2828942==    by 0x10AD64: validate (oggz-validate.c:445)
==2828942==    by 0x10A431: main (oggz-validate.c:594)

The problem is triggered when oggz_comments_decode() is calling
_oggz_comment_add_byname() with NULL as its third argument.  Not sure what should
happen with a comment consisting only of a name and no value, but the provided
patch block the crash from occuring.

Fixes #13

According to the documentation of oggz_stream_get_content(), it can
return values OGGZ_ERR_BAD_OGGZ and OGGZ_ERR_BAD_SERIALNO, neither
which is part of the return type enum OggzStreamContent.  This causes the
following compiler warning and make it impossible to check the return
value of this method without a compiler warning:

oggz_stream.c: In function ‘oggz_stream_get_content’:
oggz_stream.c:55:28: warning: implicit conversion from ‘enum OggzError’ to ‘OggzStreamContent’ [-Wenum-conversion]
   55 |   if (oggz == NULL) return OGGZ_ERR_BAD_OGGZ;
      |                            ^~~~~~~~~~~~~~~~~
oggz_stream.c:58:30: warning: implicit conversion from ‘enum OggzError’ to ‘OggzStreamContent’ [-Wenum-conversion]
   58 |   if (stream == NULL) return OGGZ_ERR_BAD_SERIALNO;
      |                              ^~~~~~~~~~~~~~~~~~~~~

This fix provide new enum members OGGZ_CONTENT_ERR_BAD_OGGZ and
OGGZ_CONTENT_ERR_BAD_SERIALNO with identical integer values as the
OGGZ_ERR_* values, ensuring ABI compatilibity while providing types
accepted by the compiler.

Fixes #16

Use PRId64 or %zu where appropriate.  Handle NULL values.

This activate several blocks of code that should compile.  Some of them did not
after the introduction of UNUSED().  Flag the arguments used with -DDEBUG
with a new macro NDUNUSED().

There are several new compiler warnings in the DEBUG protected code.  When these
are fixed, --enable-gcc-werror could be enabled for DEBUG builds to avoid
reintroducing such problems.

This avoid a compiler warning about incorrect formatting string.