Avoid confusion with the GNU extension 'program_invocation_name', which
is described by 'man 3 program_invocation_name'. The GNU version isn't
supposed to be exposed without defining _GNU_SOURCE, which we don't in
any of the relevant files, but it's best to avoid any confusion.
Some users may require a valid DEFLATE, zlib, or gzip stream but know
ahead of time that particular inputs are not compressible. zlib
supports "level 0" for this use case. Support this in libdeflate too.
Resolves https://github.com/ebiggers/libdeflate/issues/86
Move program utility functions that are used only by "test programs"
(i.e. not by gzip/gunzip) from prog_util.{c,h} into test_util.{c,h}.
This reduces the code that is compiled for the default build target,
which excludes the test programs.
QueryPerformanceCounter() is much more accurate than
GetSystemTimeAsFileTime().
Also avoid converting into a specific time unit until the results need
to be displayed. This is more efficient and avoids losing precision.
* Bring in common headers and program code from xpack project
* Move program code to programs/
* Move library code to lib/
* GNU89 and MSVC2010 compatibility
* Other changes
