Basic Stata support

Add basic Stata support. Forked and modified
github.com/drewmcdonald/stata-highlighting
Merge branch 'master' of github.com:bquistorff/highlight.js into stata
Corrected attribution of Stata by Brian Quistorff.
A longer Stata snippet.
Reset relevance of AsciiDoc smart quotes to not step on Stata.
Remove `end` from Stata snippet.
Using standard comment modes in Stata.
Adding Stata to scientific category.