Unittest add.

This one makes sure that sSCOPE_EXIT blocks are executed in the
correct order when a function is returning/exiting.
Function added: skit_error_code_to_cstr
Added SSIZE_MIN to portable_ints.
Function added: skit_pfile_slurp_into
Also some small documentation fixups in skit_pfile_stream.
Added find/partition functions in string.h.
Added the skit_pfile_stream_use_handle function.
This was needed to be able to use a skit_pfile_stream with
an already-opened FILE object that was obtained using popen.
Fix buffering logic bug in skit_stream.
This would send unallocated memory into a stream's slurp command
which, in the case of skit_pfile_stream, caused it to read file
contents into invalid memory.  This infrequently caused access
violations.
PEG Parser: Fix the success rule.
Previously, the success rule would match the entire remaining
text to be parsed.  This is almost always NOT what one would want,
because it causes parses to terminate prematurely and prevents other
rules from parsing the rest of the text.
Now, the success rule will create a zero-length match instead.
PEG Parser: Add the "end_of_text" rule.
PEG Parser: Improve parse tracing messages.
This is extremely useful for debugging parses of large bodies of
text, since it will only display the line being parsed when
entering/leaving a rule, rather than displaying the /entire/
document for /every/ rule (twice).
Bugfix in skit_trie.
This fixes a situation where case-insensitive lookups would fail
whenever two different keys shared a common prefix followed by
a single character that differs only in casing and the lookup tries
to access one of them (the wrong one, whichever that may be).
The solution was to allow case-insensitive matches to backtrack
on match failures and attempt alternative casing decisions at
every branch caused by casing differences.
Add skit_empty_stream.
Fixed a return-value corruption bug in sRETURN.
Make it possible to pass parameters to CC when using COMPILE_ALL.COM on VMS.
Added a compile-time configurable date/time parser generator.