Move installing of piqic "make install" to "make ocaml-install"

... because "piqic" is now ocaml-specific (and soon to be renamed piqic-ocaml)
Add Motiejus Jakštys to THANKS
Add support for travis-ci service

This allows running tests on shared continuous integration testing
service travis-ci.org. Currently it does:
1. compile
2. run tests (incl. ones that require protobuffers)