create .travis.yml

Tests should be passing in 3.4, but failing in 3.3 and 3.2.
travis needs to install realpath
travis needs to install flake8
add a travis badge to README.md
compat.makedirs
store PLUGINS_DIR at load time

With this commit, peru is Python 3.3 compatible again.
avoid subprocess.DEVNULL (for 3.2 compatibility)
compat.indent()

With this diff, peru is compatible with Python 3.2.
test_compat.py