fixed bug in name of error_info typedef
Fix for Trie roots.
AddressState -> Account.
Full documentation for Account class.
Minor comments.
Merge branch 'develop' of github.com:ethereum/cpp-ethereum into develop

Conflicts:
	libethereum/Executive.cpp
Merge remote-tracking branch 'upstream/develop' into bugfix
Renamed storageOverlay() to storage() in Account.h