Docstring fixes

Conflicts:
	helm-dash.el
Work on OS X too, with the original Dash
Fix byte compilation warnings, largely by using cl-lib throughout
Use the standard string-prefix-p instead of helm-dash-string-starts-with
Place custom vars in custom group
Prefer defalias to fset
Avoid return/cl-return
Don't use (removed) helm-dash-ends-with in tests
Don't test now-removed helm-dash-some
Fix indentation