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-gpg-verify-result.c

@@ -27,7 +27,7 @@
 #include "ostree-gpg-verify-result-private.h"
 
 /**
- * SECTION: libostree-gpg-verify-result
+ * SECTION: ostree-gpg-verify-result
  * @title: GPG signature verification results
  * @short_description: Inspect detached GPG signatures
  *