Implement draft11
Merge pull request #19 from todesschaf/wip/draft11

Implement draft11
README: updating the code coverage stats.
Update version number and spec references
Handle data frame compression

- We do not allow data frame compression (the default)
- We will never send compressed data frames, even if the setting is
  enabled.
Update for the new priority scheme

All trees, all the time (with weights!)
Add barebones support for BLOCKED frame

- We will not send BLOCKED
- We do not do anything when we receive BLOCKED
Update HISTORY
Update code coverage in README
Merge pull request #20 from todesschaf/wip/draft12

Implemented draft-12.
Flow: sending BLOCKED frame when appropriate
Flow tests: checking frame size validity in test scenarios
Release of version 0.12.1