Merge pull request #4 from avsm/master

add sexp representation
Merge pull request #5 from avsm/master

release 1.4.0
Merge pull request #6 from avsm/master

release 1.4.1
Merge pull request #7 from avsm/master

bump version to 1.5.0, since the Re_str dependency removal can break ups...
travis: use mirage-repo to test new packages