Mega-commit to document the API with doxygen.

Some changes were made to the API when making the documentation:

- A few exported functions are now hidden, because they were only used
  internally in the library.
- A few exported symbols were renamed to document them better than
  previously.
- Cosmetic changes all along the way, as well as some fixes here and there.

--HG--
extra : convert_revision : xtraeme%40gmail.com-20100121021019-onbsivlrhdb7t3ou

lib/config_files.c

@@ -32,7 +32,7 @@
 
 #include <xbps_api.h>
 
-int
+int HIDDEN
 xbps_config_file_from_archive_entry(prop_dictionary_t d,
 				    struct archive_entry *entry,
 				    const char *pkgname,