doc: Add OstreeMutableTree, other minor doc updates

doc/ostree-docs.xml

@@ -21,6 +21,7 @@
 		<title>API Reference</title>
 		<xi:include href="xml/libostree-core.xml"/>
 		<xi:include href="xml/libostree-repo.xml"/>
+		<xi:include href="xml/libostree-mutable-tree.xml"/>
 
 		<index id="api-index-full">
 			<title>API Index</title>

doc/ostree-sections.txt

@@ -51,6 +51,7 @@ ostree_commit_get_parent
 
 <SECTION>
 <FILE>libostree-repo</FILE>
+OstreeRepo
 OstreeRepoMode
 ostree_repo_new
 ostree_repo_new_default
@@ -90,6 +91,7 @@ ostree_repo_delete_object
 OstreeRepoCommitFilterResult
 OstreeRepoCommitFilter
 OstreeRepoCommitModifier
+OstreeRepoCommitModifierFlags
 ostree_repo_commit_modifier_new
 ostree_repo_commit_modifier_ref
 ostree_repo_commit_modifier_unref
@@ -113,3 +115,20 @@ ostree_repo_prune
 OstreeRepoPullFlags
 ostree_repo_pull
 </SECTION>
+
+<SECTION>
+<FILE>libostree-mutable-tree</FILE>
+OstreeMutableTree
+ostree_mutable_tree_new
+ostree_mutable_tree_set_metadata_checksum
+ostree_mutable_tree_get_metadata_checksum
+ostree_mutable_tree_set_contents_checksum
+ostree_mutable_tree_get_contents_checksum
+ostree_mutable_tree_replace_file
+ostree_mutable_tree_ensure_dir
+ostree_mutable_tree_lookup
+ostree_mutable_tree_ensure_parent_dirs
+ostree_mutable_tree_walk
+ostree_mutable_tree_get_subdirs
+ostree_mutable_tree_get_files
+</SECTION>