Add support for relative geometry.

[osandov]

Currently, supporting a single dzen configuration across multiple computers can be a pain because the computers might have different display resolutions. This patch adds support for specifying the size and position of the dzen window relative to the resolution by specifying a percentage (e.g., dzen -w 50% will start a dzen window taking up half of the screen width-wise).

(Resubmitted because the last pull request was a mess.)

[dpnova]

This is great... any reason why it's not being accepted?

[osandov]

This project doesn't seem to be active anymore :(

[dpnova]

@osandov cheers - hard job to get repos to accept a fork of such a well known project... might just have to build myself!