* port simple_sync across from testnet1, sync head & improved fork handling
* introduce new sync_head for tracking header chain during sync
* add debug logging in body_sync for state of various heads
* update header_head during sync if header is now the one with most work, pass in sync and head contexts to pipe
* port across sync_head changes from master, put the 1s sleep back in...
* let sync run even if the full 512 headers are all known, give sync a chance to sync against a fork that forked a long time ago
* handle height jumping during a reorg
block validaton should not check for height+1 based on head
no assumptions should be made about height indices
* quick(er) check for previous block in process_block (we cannot check height against ctx head)
* make body_sync a _lot_ faster by finding the forked block more efficiently...
* fix monitoring peers log msg
* fix chain tests
* fix grin tests - we were using the wrong genesis hash (wrong chain type)
* apparently needs setting in both places...
* body -> header -> sync (#414)
* port over body -> header -> sync changes from testnet1
* rename pubkey -> key_id, these are key identifiers, not public keys
* reduce identifier seize to 10 bytes, get rid of fingerprints (identifiers are now small enough to use as-is)
* IDENTIFIER_SIZE const
* add FeeDispute error for when sender and recipient disagre on fee calculation (should never happen)
* does not need to be mut
* cleaned up some warnings
* store wallet output data in hashmap
* cleanup up commented out code
* pass pubkey/identifier and not derivation around to miner etc.
* fix failing tests
* introduce grin_keychain, encapsulate derivation of secret_keys
* core compiles against keychain, tests don't run yet
* core tests are now passing against keychain
* wip - getting wallet working with keychain
* add util and keychain to travis test matrix
* basic test around key derivation
* initial pass at indexing block header hashes by commitments
* check block height matches currently indexed block height
when getting block header for an output commit
* add some test coverage
* document get_block_header_by_output_commit
