Improved pkg best matching in rpool, and support for exact pkgver matches.

- xbps_repository_pool_find_pkg in best match case, now returns the
  newest package version available in rpool.
- Added xbps_repository_pool_find_pkg_exact that returns a package
  by exact matching a pkgver.
- Removed xbps_handle_alloc(), the user is free to use memory
  allocated from heap or stack.
- Improved API documentation in preparation for 0.12.

Bumped XBPS_API_VERSION again.

lib/package_state.c

@@ -57,9 +57,6 @@ static int
 set_new_state(prop_dictionary_t dict, pkg_state_t state)
 {
 	const struct state *stp;
-#ifdef DEBUG
-	const char *pkgname;
-#endif
 
 	assert(prop_object_type(dict) == PROP_TYPE_DICTIONARY);
 
@@ -73,13 +70,6 @@ set_new_state(prop_dictionary_t dict, pkg_state_t state)
 	if (!prop_dictionary_set_cstring_nocopy(dict, "state", stp->string))
 		return EINVAL;
 
-#ifdef DEBUG
-	if (prop_dictionary_get_cstring_nocopy(dict, "pkgname", &pkgname)) {
-		xbps_dbg_printf("%s: changed pkg state to '%s'\n",
-		    pkgname, stp->string);
-	}
-#endif
-
 	return 0;
 }