Merge pull request scylladb#225 from dkropachev/dk/add-iter-docs

Add iterator docs

Merge pull request scylladb#178 from sylwiaszunejko/unix_socket

Fix setting up connection to non-IP sockets

Merge pull request scylladb#168 from sylwiaszunejko/avoid_slow_replicas

Add LOAD_BALANCING_POLICY_SLOW_AVOIDANCE funtionality

Merge pull request scylladb#158 from sylwiaszunejko/debug_scylla_bench

Fix checking if tablets should be used in scyllaConnPicker Pick

Merge pull request scylladb#152 from sylwiaszunejko/aggregate_bug

Fix aggregate bug

Merge remote-tracking branch 'gocql/master'

Merge pull request scylladb#139 from avelanarius/retract-versions

Retract tags taken by mistake from kiwicom/gocql

Add configurable MaxRequestsPerConn cluster param

Before this change, a connection had a hardcoded maximum number of
streams. Since this value was so large (32768 for CQL v3+) this
essentially meant an unbound concurrency.

This commit allows a user to configure this parameter by a newly
added MaxRequestsPerConn option.

The "MaxRequestsPerConn" naming was chosen to be very general
deliberately to allow us to safely introduce a more advanced behavior in
the future: where the concurrency limiting happens not at a IDGenerator
level and an additional client-side queue is introduced for requests
to wait to be sent to Scylla (in addition to inflight requests).

This commit deliberately does not change the defaults as to be
non-pessimizing for the users.

Fixes scylladb#112

Make heavy loaded optimization configurable

Scylla Go Driver has a capability to avoid sending requests to an
overloaded shard, instead sending the request on a different connection
(at the same node).

This change makes it possible to customize the parameters used to
determine when this behavior would kick in.