Fix minor issues found with Cppcheck
Simplify creating test context

Now separate functions are used to set different things. This removed a
lot of variables from main().
Test context does not need test directory
Do not use timersub function

This commit introduces equivalent function time_difference that does the
same thing but is always present.
Make compilation with -c99 -pedantic succeed

This required adding a few feature test macros. However, the test suite
emits huge amount of warnings.
Explicitly mark no argument functions as such
Only print bold on stdout, not into files
Add man page for stest

The page is populated with package name, version and bugreport address
during configure step.
Add man page for gen-test
Update README
Include config.h as first thing in every file
Define _POSIX_C_SOURCE in config.h
Clean up header includes

Local includes are now before system ones. Also reduce number of
included files by removing some redundant ones.
Do not version config.h.in

It is generated by autoreconf, so there is no need to store it in git.
Fix a typo in README
Print summary after configuring
Set -Wall through AM_CFLAGS
Use explicit .gitignore in m4/
Move detecting -Wall to separate file

Now configure.ac only needs CC_HAS_WALL macro to enable -Wall (if
supported).