more nomials refactoring
more nomials refactoring

 - new equalities (now eid- and c- instead of string-based)
 - cleaner and faster simplify code
 - use of defaultdicts for eid (means that any non-named variables returns
   a 0 instead of an error)
 - removed non-dict interface to making a monomial

galbramc/gpkit,convexopt/gpkit,convexopt/gpkit,galbramc/gpkit,hoburg/gpkit,hoburg/gpkit