Moved sync out of ethcore crate; Added block validation

RLP encoder refactoring

Chain sync tests and minor refactoring

Common log init function

changed max vm depth from 128 to 64, change homestead block to 1_000_000

Conflicts:
	src/tests/helpers.rs

fixed blockchain tests crash on log init

Blockchain tests and some helpers for guarding temp directory

Fix logging and random tests.

Fix random blockchain tests.
Closes #249

Fix difficulty calculation algo.