Add support for CTX

[wadearnold]

CTX Corporate Trade Exchange
The Corporate Trade Exchange (CTX) application provides the ability to collect and disburse funds and information between companies. Generally, it is used by businesses paying one another for goods or services. These payments replace checks with an electronic process of debiting and crediting invoices between the financial institutions of participating companies.

Record format specification
http://docs.moov.io/en/latest/ACH_File_Structure/#ctx-corporate-trade-exchange

[wadearnold]

closed #231 commit