Added Xtend (xtend-lang.org) to languages.yml
Added samples for Xtend
Update lib/linguist/languages.yml

added primary_extension: .xtend
Add .editorconfig as an INI file

See http://editorconfig.org
Merge pull request #399 from BPScott/add-editorconfig

Add .editorconfig as an INI file
Merge pull request #342 from svenefftinge/master

languages.yml: add Xtend