Prerequisites for tntcxx release

[Korablev77]

TODO:

• Fix Clang build (2 sp)
• Fix Release build (1 sp)
• Fix OSX build: there's no epoll, so we'll have to rewrite network engine a bit (7 sp)
• Provide unified syntax for CMAKE (0.1 sp)
• Make all possible arguments templates (1 sp)
• Provide restriction for number of requests in a single connection in order to remove dynamic allocations (i.e. remove std::map of request id -> response and introduce static/stack hash map) (2 sp)
• Remove std::optional usages: use std::variant for response content (2 sp)
• Close connection in the destructor of class Connection (0.5 sp)
• Remove exceptions from base64 decoder (0.5 sp)
• Provide wrappers for synchronous methods (now connection is purely asynchronous) (2 sp)
• Provide virtural logger (so that users may embed their own logger; current one simply prints output to stderr/stdout) (2 sp)
• Provide an ability to ignore responses for certain requests (2 sp)
• Rework Connector::waitAny method: now it returns connection, but still not futures which are ready to decode (1 sp)
• Provide more perf tests (e.g. with different buffer's sizes) (3 sp)
• Provide more unit/integration tests (e.g. simulate broken connection, broken msgpack responses, different schema versions etc) (5 sp)
• Add missing request types (15.5 sp in total):
• get (0.5 sp)
• update/upsert (2 sp)
• delete (0.5 sp)
• grants (2 sp)
• eval (1 sp)
• sql (5 sp -- a bit more complicated: need to support different response type (metadata), prepare/execute requests)
• wrappers for DDL (2 sp)
• Add authentication processing (now salt is stored but not used) (1 sp)
• Add more complicated examples of tuple readers (with same field types, with array/map types) (1 sp)