Fix builds that fail on Heroku.

* Specs for language detection

* Use CharlockHolmes instead of NKF

* Correct mistakes

* Correct style

* Set hint_enc instead of falling back and strip_tags

* Improve specs

* Add dependencies

This change adds mp4 support confirmed on Heroku-16 stack.

Use https://github.com/heroku/heroku-buildpack-apt to
install protobuf-compiler and libprotobuf-dev which are needed by cid3