Initial effort to add Bitfinex Total Return Swaps capability to XChange.
This implementation currently has tested the raw functions related to 
getting the active swaps order book, sending offers (a swap order in BFX
API terminology), retrieving responses, and cancelling offers. This work
has not been exposed through the generic TradeServices as I would like
to make sure that it is acceptable to add these loan types to the
generic interfaces (and have a bunch of NotImplementedExceptions).
Merge remote-tracking branch 'upstream/develop'

Conflicts:
	xchange-bitfinex/src/main/java/com/xeiam/xchange/bitfinex/v1/service/polling/BitfinexTradeServiceRaw.java
Implement BTCChina getMarketDepths API method.
Fix warning in javadoc for BTCChina module.
Add license header.
Test
Public Market Data Implementation
Merge branch 'develop' of https://github.com/zholmes1/XChange into develop
Bittrex Public Market Data Implementation
Bittrex Public Market Data Implementation
Begin Implementing PollingAccountService
Begin Implementing PollingAccountService
Fixed getbalances path
Add example lend book demo
Make sure the print statement accurately describes the USD swap order
book
Include appropriate MIT header
ensure comment correctly states BFX as the exchange we're retrieving the
instance of.
Added BTER User Trade History
Full Bittrex Implementation

Implemented Bittrex public and authenticated methods. Also added a
builder for LimitOrder
Full Bittrex Implementation