Terminals are described with their names.
Name the terminals in the parsing tests.
Combinators can be pretty-printed.
Nonterminals pretty-print.
Nonterminal descriptions abbreviate named parsers.
Abstract pretty-printing to a string.
Merge pull request #64 from robrix/pretty-printing

Pretty printing
Merge branch 'master' into lexer

Conflicts:
	Hammer/HMRNonterminal.m