docs: Get API docs working again

This changes around a few things that didn't work for me:
* Section names seem to be ostree-* instead of libostree-*
* Also XML files are ostree-* (they didn't show up at all)
- gtk-doc doesn't seem to parse const _OSTREE_PUBLIC correctly
* pull documentation is now on the actual functions rather than stubs
* Update gitignore with some more files

And there some changes to make gtk-doc give fewer warnings (not finished)

Closes: #327
Approved by: cgwalters

src/libostree/ostree-core.c

@@ -47,7 +47,7 @@ zlib_file_header_parse (GVariant         *metadata,
                         GError          **error);
 
 /**
- * SECTION:libostree-core
+ * SECTION:ostree-core
  * @title: Core repository-independent functions
  * @short_description: Create, validate, and convert core data types
  *