Use shebang lines of scripts to determine language

The first of these commits add a new `interpreters` array to languages.  When determining the language of scripts, the Shebang lines are parsed to find the interpreter used which may be matched against known interpreters to determine the language.  Works in local tests for scripts which are mis-classified by the current version of linguist.

The second commit populates the `interpreters` arrays for a number of languages.

The third commit adds the sed programming languages as the impetus for this change was a sed script misclassified as perl (which is a pretty good guess).

Cheers,