Add earthquake information segment

I considered just using this myself since the audience would be limited,
but because it is a non trivial problem I have decided to ask you if you want
to add it to the main tmux-powerline repository.

I always find myself checking the earthquake alert system whenever
I feel a tremor. Here is a segment that can do that for me right in tmux.

This segment currently only looks at the 'goo' earthquake rss feed,
which takes it's information from the Japan Meteorological Agency.
This segment can be customized to display recent earthquakes that occur
in a given 'alert-window' above a certain magnitude threshhold. This
information should not and cannot be used as an early warning system,
but is helpful in alerting you to large quakes that may have happened
nearby.

It is not turned on in the default theme because mostly only people in Japan 
would use it.

This relies on goo's rss text formatting which is human-readable and not computer 
readable. If the format changes, this will break. I don't see that happening any time
soon though.