some tests for Envelope class done
1. Added precautionary tolerances to all double-double comparisons (from a < b to a-b < EPSILON for some tolerance level EPSILON)   2. Rearranged all references to different coin types to put dollars - the largest values - at the front rather than at the back (adjusted the tests to fit)   3. Changed variables to avoid multiple variables called 'value' or 'values'.   4. Adjusted the Envelope Comparison tests: -1 should mean less than, and +1 should mean greater than, right?
Added integer-returning getValue functions, for Cashier's use
Added skeleton for Cashier and the exception class - put in tests for the Cashier Test - corrected spelling of 'nickel'
Small edit to Negative Balance Exception
some small change
merging nathan into master
refactored addMoney to match params of takeMoney...all tests pass