Makefile: Do not pass header as a standalone input for the compiler.
cutest.h: Fix subprocess start on Windows.

On Windows 8.1, we passed only pseudo-handles of stdout and stderr,
hence the subprocess was always silent.
cutest.h: Set default verbose level to 2 and ...

... make info about passed conditions use verbose level 3.
cutest.h: Fix comment typo.
cutest.h: Update copyright info.
cutest.h: Use standard header guards.
cutest.h: Introduce support for TEST_NO_MAIN.

This allows to suppress generatiion of main() in case of
multiple compilation units.