Allow providing connection config to DialTLSWithConfig
DialConfig parameterizes connection config

No more magic contructors left during transport setup.  This should be
simpler instead of requiring the application to setup the transport then
use Open(rwc, config).
Merge remote-tracking branch 'torkale/dial_config' into 86-dial-config

Alternative implementation to torkale/dial_config

Conflicts:
	connection.go
Documentation of Config

Now that Config works for both Dial and Open, some of the fields have
picked up defaults from the Dial path.
Merge pull request #87 from streadway/86-dial-config

DialConfig for generalized transport + connection