karma: move Travis configuration into config file

This let's us shorten the command lines in the Travis config file and
better reuse/edit the configration later.
karma: run without coverage by default

Coverage generation slows down what is supposed to be very fast
continiously running tests.
npm: add coverage script

This runs Karma and continiously generates coverage data.
travis: send coverage data to coveralls.io

This is a free service that will host the generated coverage reports.
It will also comment on open pull requests with info about the change
in coverage caused by that pull request.

The reports will show up at:

  https://coveralls.io/r/zerovm/swift-browser
readme: add coveralls badge
Merge pull request #14 from mgeisler/coveralls

Send coverage data to coveralls.io