Slightly higher level macro support

TODO:
Macros return a list of symbols so allow the generation of a list of
symbol to proceed as easily as the generation of a STRING of mocha-script
code.
Exploration of more abstract macro definition
Vastly simplified the backtick operator for macros -- but:

We need to fix / update the grammar.  It should just produce exps and
sexps and not much else.  The processors/macros should handle the rest.
Removed conflicted parts of the grammar until it is refactored.
Greatly simplified the grammar
Macro examples