json tests are not run in default configuration, faster travis build, fixed coverage for ethcore-rpc and ethash

fixed building docs

update travis to build PRs only against master

Coverage effort

updated docker containers

Conflicts:
	ethcore/src/receipt.rs

rpc module fixes

Test for Receipt RLP.

Building from source guide

Fixed neted empty list RLP encoding

Fix CALLDATACOPY (and bonus CODECOPY, too!).

added travis && coveralls badge to README.md

Reorder Stage 4 verification to check easier things first.

coveralls coverage

Fixes #269
Fixes #270
Also fix evm debug feature.