Add a pressgang-log command

[xsgordon]

To make full use of the ability to retrieve specific revisions of a topic users are going to want access to the list of revisions for a topic. I'd like it to mimic git's output format by default:

$ pressgang-log 10007
revision: 5
Author: sgordon
Date:    Fri Nov 23 16:42:28 2012 -0500

    My changelog message.

revision: 4
Author: juggernaut
Date:    Fri Nov 23 14:38:22 2012 -0500

    The Juggernaut's message.

Unlike GIT however I'm not sure we should use a pager by default. If we do then we should support the --no-pager option. By default git-log supports a lot of other options which I do not believe are necessary in this initial implementation.

To start with though I would be interested in supporting as many of these as possible:

• **-n / --max-count to limit the number of commits to output.
• --skip to skip a number of revisions before starting output.
• --since / --after to only show revisions after a certain date.
• --until / --before to only show revisions before a certain date.

Additionally I would like to add an additional --quiet option which would just output the log in this format:

$ pressgang-log 10007
revision: 5, Author: sgordon, Date: Fri Nov 23 16:42:28 2012 -0500
revision 4, Author: juggernaut, Date: Fri Nov 23 14:38:22 2012 -0500

[xsgordon]

Pressgang now supports this style of URL to retrieve a specific revision:

TopicIndex/seam/resource/rest/1/topic/get/xml/10007/r/225566/xml