* fixed encoding 0u8

* simplified if else stmt

* tracedb core

* more comprehensive tracedb tests

* fixed minor review issues

* addresses filter

* fixed typos

* replace malformed with corrupted

* trace switch

* db key is generic and can be made smaller

* smaller tracedb keys

* tracedb version

* fixed ignored tests

* rename Tracedb -> TraceDB

* fixed typos

* proves

* trace only top level calls to builtins to avoid DDoS attacks

* fixed tracedb config switches

* fix comments fat replaced with trace

* vector-addressing scheme for localized traces

* removed comments

* removed first, redundant 0 from trace address

* updated db.trace method

* additional tests for tracedb.trace()

* Support `pending` block in RPC

* Forward calls from miner to client in case no pending block is available

* removed redundant unwraps

* fixed compilation error, removed warnings

* fixed transaction queue merge conflict

* fixed failing ethminer doc test

* spec loading cleanup in progress

* changed engine field in json spec

* refactored engine params

* polishing spec loading refactor

* fixed compiling json tests

* fixed compiling parity

* removed warnings

* removed commented out code

* fixed failing test

* bringing back removed TODO in spec.

`ClosedBlock`s still keep the pre-finalised state (i.e. state after the last transaction).
`LockedBlock`s do not. New mining algo needs to reopen these `ClosedBlock`s, however enactment
system does not (and `ClosedBlock`s are slower & more hungry), hence the distinction.

Fixes #756.

Docuemnt SealingWork properly.