Added common alternative Handlebars extensions
Needed handlebars extensions in alpha-numeric order.
Add LaTeX and BibTeX
Update languages.yml
Update languages.yml
Add definitions to TeX
TypeScript: fixed syntax, it wasn't TypeScript at all
Highlight .jelly files as XML

[Jelly](http://commons.apache.org/proper/commons-jelly/) is used heavily by stapler/stapler and jenkinsci/jenkins.
add @primary_extension_index to ensure we don't have duped primary exts
use @primary_extension_index in find_by_filename
change MUMPS' primary extension from .m to .mumps

.m currently clashes with Objective-C, and MUMPS is chosen before
Objective-C when creating .m files in Gist. Even if .mumps isn't a
legitimate MUMPS extension, I think we should change it anyway since
Objective-C is far more likely to be intended when a user uses .m
add .m as an alternate extension for MUMPS so it's still picked up
update samples.json
Merge pull request #728 from github/fix-dup-primary-extension-for-mumps

Ensure no two languages have the same primary extension
Merge pull request #701 from thorn0/patch-1

TypeScript: fixed syntax, it wasn't TypeScript at all
Merge pull request #721 from olivergondza/patch-1

Highlight .jelly files as XML
Merge pull request #663 from acgetchell/patch-2

Add LaTeX and BibTeX
Merge pull request #584 from jayphelps/patch-1

Added common alternative Handlebars extensions