Add defcallback snippet.
Add defmacrocallback snippet and addition to syntax list for highlighting.
Add defdelegate snippet.
Add snippet for defexception, with replaceable :message atom as default.
Add snippet for defoverridable with placehoders for a keyword list.
Add snippet for defprotocol.
Add defstruct snippet with omitted brackets, since this seems to be the popular norm.
Merge pull request #24 from ybakos/def_snippets

Add snippets for various defs
Added mix test build

Added the mix test build command. Currently will execute the test at
the root of the project director in sublime.
Merge pull request #25 from ot-joe-ocampo/master

Added mix test build