setup basic tests for continuous integration (using travis)

setup .travis.yml and default scripts to enable automatic testing
on travis-ci infrastructure.
make eslint happy

this should make the test on travis-ci.org pass. Acually, this is a work-around
rather than a fix, because it would have been quite cumbersome to add
"use strict" statements everywhere. This would lead to merge conflicts, and the
benefit is not that high. Once switched to a module system, this check can be
enabled, again.
add build status batch to README.md

useful to see the build status of the current master branch, which should
always show "green", once enabled.
Merge pull request #91 from johnyb/travisci

enable Travis CI