Backfill spdy and http/2 related tests wrt zero-length messages.
Merge pull request #480 from adriancole/backfill-tests

Backfill spdy and http/2 related tests wrt zero-length messages.
Create concurrency doc.
Improve some Markdown
Style fixes
Honor connection-level flow control for writes.

We don't write until the peer has given us a budget.
Merge pull request #482 from square/jwilson_0126_flow_control_writes

Honor connection-level flow control for writes.
Honor change in connection-level initial write window from peer settings.
Merge pull request #483 from adriancole/connection-settings-changes-write-window

Honor change in initial write window from peer settings.
spdy streams honor write window updates.
Merge pull request #484 from adriancole/stream-window-update

spdy streams honor write window updates
OkBuffer API sketch.

I'm unhappy with java.io:
 * No timeouts.
 * Every layer needs to copy bytes around. Always copying bytes.
 * Features like mark/reset and available() are clumsy.
 * Its awkard in mixed text/binary protocols like HTTP because
   character decoding is separate and takes over the stream.

Unfortunately java.nio isn't better, just different:
 * It's complex.
 * Buffers are fixed size.
 * No built-in buffer pooling.
 * Features like mark/reset/position are clumsy.

This is an obnoxious attempt at a 3rd I/O interface, mostly
inspired by InputStream and OutputStream, but using growable
buffers instead of byte arrays as the core data container.
Merge pull request #485 from square/okbuffer

OkBuffer API sketch.
Implement moving bytes between OkBuffers.

This is more complicated than I'd anticipated.
Merge pull request #487 from square/jwilson_0126_buffer_to_buffer

Implement moving bytes between OkBuffers.
Send window update after the peer sends half the limit on a stream or connection.
Fix mockwebserver jar download 404
Merge pull request #486 from adriancole/window-update

Send window update after the peer sends half the limit on a stream or connection
Merge pull request #488 from jgilfelt/patch-1

Fix mockwebserver jar download 404
Test de-flakiness attempt

Update surefire to latest and set travis to emit maven version.

Only use one MockSpdyPeer in SpdyConnectionTest and close its executor.

Consistency in HttpURLConnection tests.

Bump so and read timeouts in ConnectionPoolTest.