Reimplement fast forward

[renecannao]

Following the implementation of fast forward, it was disabled after writing http://www.proxysql.com/2015/06/sql-load-balancing-benchmark-comparing.html and commenting I would always use ProxySQL's query processing that implements important features .
In other words, a fully featured ProxySQL is faster than other proxies out there with very limited features.
Although, for several reasons, fast forward mode is being reintroduced again:

• reach high performance when complex features aren't required , and benchmark
• draft support for unsupported part of the protocol (prepared statement, see Prepare Statements in mysqli for php fail #444)

Closes #256
Closes #264
Closes #265
Closes #300