Errors shown as warnings & new invalid arg error

new features:
- Errors use: echohl WarningMsg  rather than echohl ErrorMsg
- display an error when  invalid arguments are used
- New Function EchoError()

style changes:
- references to '<args>' changed to <q-args>
- include checking if arguments exist in s:HandleArgs()
Style: crunch#Crunch... changed to crunch#Eval...