versioned_graph/commit

improved: pldoc

diff --git a/lib/graph_version.pl b/lib/graph_version.pl
index c3ee16d..732a811 100644
--- a/lib/graph_version.pl
+++ b/lib/graph_version.pl
@@ -12,6 +12,11 @@
 	    gv_init/1		      % +Options
 	  ]).
 
+/** <module> Versioning named graphs
+
+@author Jacco van Ossenbruggen
+*/
+
 :- use_module(library(semweb/rdf_db)).
 :- use_module(library(semweb/rdf_label)).
 :- use_module(library(settings)).
diff --git a/lib/parse_git_objects.pl b/lib/parse_git_objects.pl
index 67f9cd1..a4c0477 100644
--- a/lib/parse_git_objects.pl
+++ b/lib/parse_git_objects.pl
@@ -1,11 +1,36 @@
 :- module(gv_parse_git_objects,
-	  [
-	  commit//1,
-	  tree//1
+	  [ commit//1,
+	    % tag//1, % TODO
+	    tree//1
 	  ]).
+/** <module> Parse git commit and tree objects.
+Parse commit and tree objects from their git serialisation. Note that
+blob objects can be directly parsed using rdf_read_turtle/3.
 
+@todo: parse git tag objects
+
+@author: Jacco van Ossenbruggen
+*/
 :- use_module(library(semweb/rdf_db)).
 
+%!	tree(List)// is semidet.
+%
+%	List is property list [hash(H), name(N)].
+
+tree([H|T]) -->
+	blobline(H),!,
+	tree(T).
+tree([]) --> [].
+
+%!	commit(Commit)// is semidet.
+%
+%	Commit is a property list consisting of
+%	* tree(T)
+%	* parent(P)
+%	* author(A),
+%	* committer(C)
+%	* comment(M).
+
 commit(Commit) -->
 	tree_line(T),
 	parent(P),
@@ -138,15 +163,6 @@ xdigit(E) -->
         { code_type(E, xdigit(_))
         }.
 
-
-
-
-
-tree([H|T]) -->
-	blobline(H),!,
-	tree(T).
-tree([]) --> [].
-
 blobline(Blob) -->
 	mode,
 	myblob,
diff --git a/lib/url_to_filename.pl b/lib/url_to_filename.pl
index c265160..f248cee 100644
--- a/lib/url_to_filename.pl
+++ b/lib/url_to_filename.pl
@@ -5,7 +5,7 @@
 :- use_module(library(url)).
 :- use_module(library(lists)).
 
-%%	url_to_filename(-URL, +FileName) is det.
+%!	url_to_filename(-URL, +FileName) is det.
 %
 %	Encode a valid URL into a valid filename and vice versa. Earlier
 %	versions used www_form_encode/2, but this can produce characters