Lastest 2.1.3 features

After a long time of code-only activity, I decided to briefly describe most recent changes and features in sphinxclient library. This refers to libsphinxclient6 v. 2.1.3.

• There is a possibility to run multiple queries asynchronously, reducing the latency of search. This can be done automatically, when the library detects, that given queries cannot be optimized to a single sphinx multi-query (because of different query or filters or select clause).
• Some interface tuning.
• Improved network error handling and retrying.
• Added support for MVA64 attributes.
• Added support for string attributes.
• Added support for new sphinx ranking modes.
• Dropped support for sphinx 0.9.8 and older.