Defaulting to no-push via SETTINGS_MAX_CONCURRENT_STREAMS

[OsamaM]

This is fork of issue #38 to focus on discussing "defaulting to no-push."

The thinking is that client and server endpoints should have different minimum values and default values for SETTINGS_MAX_CONCURRENT_STREAMS.

From issue #20 we understand that SETTINGS_MAX_CONCURRENT_STREAMS is directional and a client can advertise a value of 0 to prevent the server from issuing Push Streams.

The suggestion is that the default value should also be 0. That is, the communication defaults to no-push. If the client is sophisticated then it can advertise a non-zero value in its initial SETTINGS frame to allow the server to push.

[mnot]

DIscussed in SF Interim; decided to wait until we have more implementation experience.

[martinthomson]

With the changes to include HTTP2-Settings, the server never sends frames in ignorance of the clients settings. Rather than deferring, can we close this @OsamaM ?

[OsamaM]

Solved via "HTTP2-Settings Header Field" section.