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-mutable-tree.h

@@ -84,7 +84,8 @@ gboolean ostree_mutable_tree_lookup (OstreeMutableTree   *self,
                                      OstreeMutableTree  **out_subdir,
                                      GError             **error);
 
-_OSTREE_PUBLIC gboolean
+_OSTREE_PUBLIC
+gboolean
 ostree_mutable_tree_ensure_parent_dirs (OstreeMutableTree  *self,
                                         GPtrArray          *split_path,
                                         const char         *metadata_checksum,