Order-book

* Feature: Checksum support for orderbooks
* Feature: FTX checksum support
* Feature: Kraken checksum support
* Feature: OkEX/OKCoin checksum support
* Perf: Use CRC32 table to improve performance of checksum code

* Minor: Use enums to make code more readable
* Bugfix: Add manifest file to ensure headers and changes file are included in sdist builds
* Feature: Add support for max depth and depth truncation

* Bugfix: Fix sorted dictionary arg parsing
* Feature: Coverage report generation for C library
* Bugfix: Fix reference counting in index method in SortedDict
* Feature: New unit tests to improve SortedDict coverage
* Feature: Modularize files
* Feature: Add ability to set bids/asks to dictionaries via attributes or \[ \]
* Docs: Update README with simple usage example

* Initial Release