* WIP - split the key in final tx step
store "offset" on transaction itself
* rebase
* commit
* tx with offset
* got a test tx validating successfully using a sig from a split key and the appropriate offset
* sum up the offset for the block_header
* fix size tests for blocks and compact blocks (header now includes offset)
* use txs with offsets in most of the core tests
some tests now failing
* build kernel from k1G (k2 stored on tx, sum stored on header)
* commit
* tx now has vec of kernels
rework tx and kernel validation
* add test for tx cut_through
* wip - working on splitting in aggsig
* split the key when creating the initial sender aggsig context
* cleanup
* cleanup
* code needs claning up but split keys working for sender/receiver aggsig flow
* cleanup debug logging
* fix tests
* fix merge and basic cleanup
* fix keychain tests to use new tx_id
* 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
* 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