core: Add a base 64 decoder.
* src/b64dec.c: New. Taken from gnupg. Prefix function names with _gpgme_ and change to use standard C malloc functions. * src/util.h.h (struct b64state): New. * src/Makefile.am (main_sources): Add file.
The file b64dec.c has been taken from gnupg commit
e430ff6ad0b7dcfcebd92b825dd5168205447ff3
- Signed-off-by: Werner Koch <wk@gnupg.org>