Make default snippet customizable
Factor out embedded elisp code

* yasnippet.el (yas--key-from-desc): Added
Assume NO-TEMPLATE is non-nil if `yas-new-snippet-default' is nil
Merge pull request #397 from thisirs/customizable-snippet

Make default snippet customizable
Merge remote-tracking branch 'upstream/master'

Conflicts:
	yasnippet.el