Add ToC

Table of Contents
Merge pull request #380 from rippler/patch-3

Add ToC
Merge pull request #381 from JahPowerBit/develop3

catch TypeError in API
Merge pull request #383 from JahPowerBit/develop3

[#382] empty util.BLOCK_LEDGER before parsing block instead after
Revert "moved singleton check to appropriate place"

This reverts commit e6ec38efc73116326cd679fb0ec9369372e25eac.
clean up consensus check
rewrite of consensus checks
merge new_consensus_checks
fix tests