Stack new template via URL

[Tehnix]

An update on stack new shows that its working on URLs commercialhaskell/stack#2681 (comment).

This means we could make a .hsfiles template in this repo and then point to that. I just tested it out on the simple template,

stack new TestServ https://raw.githubusercontent.com/commercialhaskell/stack-templates/master/simple.hsfiles

which works like one would expect.