Add Language Igor (#276)

* Add Language Igor

Igor is a scientific language developed by
[WaveMetrics](https://www.wavemetrics.com/).

This lexer was translated directly from the [pygments
lexer](http://pygments.org/docs/lexers/#lexers-for-igor-pro) without any
changes. The pygments lexer is very basic but working properly for most
of the cases.

Author: ukos-git