Add ASSERT_EMPTY macro.

Which tests that previous parse didn't produce any errors or
entries. In case this is not true, it dumps what was produced.
Print a message when certain test starts.
Add basic comment parsing test.
Add --enable-debug flag.

All it does is define DEBUG macro.
Don't go beyond \0 byte in authinfo_skip_line function.
Add basic macdef parsing test.
Handle unexpected EOF in authinfo_skip_macdef.
Don't reinvent authinfo_eol function.