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>

src/libostree/ostree-mutable-tree.c

@@ -27,6 +27,23 @@
 #include "ostree-core.h"
 #include "libgsystem.h"
 
+/**
+ * SECTION:libostree-mutable-tree
+ * @title: In-memory modifiable filesystem tree
+ * @short_description: Modifiable filesystem tree
+ *
+ * In order to commit content into an #OstreeRepo, it must first be
+ * imported into an #OstreeMutableTree.  There are several high level
+ * APIs to create an initiable #OstreeMutableTree from a physical
+ * filesystem directory, but they may also be computed
+ * programmatically.
+ */
+
+/**
+ * OstreeMutableTree:
+ *
+ * Private instance structure.
+ */
 struct OstreeMutableTree
 {
   GObject parent_instance;

src/libostree/ostree-repo-private.h

@@ -24,6 +24,11 @@
 
 G_BEGIN_DECLS
 
+/**
+ * OstreeRepo:
+ *
+ * Private instance structure.
+ */
 struct OstreeRepo {
   GObject parent;