Enhanced Amber REPL.
save previous results; Ctrl+L to clear screen
DRYed; also: assign new variables only if necessary
refactored too long repl methods
do not count up res names for no reason
refactoring: method names, multi value returns
fixed exception on empty line; generalised commands
Merge pull request #524 from machisuji/repl

Amber REPL Enhancements