language interpreters and shebang lines

Add an interpreter array to each language, and match interpreters found
in the shebang lines of scripts to this array to identify the language
of scripts.

With suggestions from tnm. https://github.com/github/linguist/pull/687
adding interpreter arrays to some languages
unit test for find_by_shebang
Merge branch 'master' into more-687
Place guards, checks for multiline shell hacks