[TASK] add npm-debug to gitignore
[TEST] add test for demurred currency Amount parsing
[FEATURE] Currency: add option force hex in json format

provide the `force_hex` flag in the options object in a `to_json` or `json_rewrite` call
[FIX] force hex for orderbook requests

interest bearing currencies would be sent down malformed `XAU (0.5%pa)` when rippled would be expecting either hex or iso
[FIX] value parsing for amount/currency order pairs

e.g. `100000 USD` and `USD 100000` should have the same result
[TEST] add full_name null case test
[TEST] modify order book test to support hex values
[FEATURE] use Currency object and hex format in orderbook

instead of checking the value of the currency string, create a Currency object and work with that
the json format going to rippled will contain the hex value of the currency
[TEST] add test to verify HEX_ZERO is native currency
Merge pull request #111 from geertweening/feature/order_book_hex

[FEATURE] use hex format for currencies in orderbook