Adjust font weight

This makes the font a little less blurry in the graph, arguably much more readable.

https://github.com/erikh?tab=overview&from=1978-12-01&to=1978-12-31 is a good example.

Origin specification

This release allows for the origin date to be specified, allowing you to target the beginning of the graph at certain dates. This is a step closer to something like "marquee mode", which I think we can all agree will be pretty awesome.