gendoc: add anchors for commands
Enables links into hg.1.html of the form: hg.1.html#command
a
b/a
l
644 a
755 * b/a
644 @ l
b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 644 a
b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 755 * b/a
047b75c6d7a3ef6a2243bd0e99f94f6ea6683597 644 @ l
a
l
a
b/a
l
a
b/a
l
% should fail
abort: unknown revision '2'!
abort: please specify just one revision
a
b/a
l