Reconnect when Cassandra connection gets an error

Tested by manually start/stopping Cassandra and using:

application:start(snappy).
application:start(lz4).
application:start(erlcql).
{ok, Pid} = erlcql:start_link("localhost", [{auto_reconnect, true}]).
erlcql:q(Pid, <<"SELECT * FROM t">>).
Return {error, not_connected} when not connected
Use https for rebar dep
Merge pull request #22 from puzza007/reconnect

Auto-reconnect features