dagparser: parses and formats DAGs as concise text
As discussed during the sprint. See the doc comment and doctests
for specification and examples. This is used in subsequent patches
to export revlog and changelog DAGs, and to generate a repo with
a given changelog DAG.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<link rel="icon" href="{staticurl}hgicon.png" type="image/png">
<meta name="robots" content="index, nofollow" />
<link rel="stylesheet" href="{staticurl}style.css" type="text/css" />