OTLedger: rename class to Ledger
OTLedger: rename files to Ledger.{h,c}pp
Merge pull request #469 from toxeus/renameOTLedger

OTLedger: rename to Ledger
OTLog: rename class to Log
OTLog: rename files to Log.{h,c}pp
Merge pull request #470 from toxeus/renameOTLog

OTLog: rename to Log
OTNumList: rename class to NumList
OTNumList: rename files to NumList.{h,c}pp
Merge pull request #471 from toxeus/renameOTNumList

OTNumList: rename to NumList
OT_ME: use C API for register_nym()
Add params for return value and its length