feature: add cross-chain input (#61)

feature: add cross-chain input (#61)

* refactor: rename files

* feat: add types.CrossChainInput

* feat: add protocol.CrossChainInput

* wip: init bc.CrossChainInput

* fix: add mainchain output hash

* fix: fix letter cases

* refactor: fix indent

* fix: fix missing value in CrossChainInput

* fix: fix NewCrossChainInput()

* wip: upgrade MapTx()

* refactor: use issue's type indicator for cross-chain input

* revert

* wip: loop Inputs in mapTx()

* wip: add crossIn.SetDestination() in mapTx()

* feat: draft mapTx()

* refactor: remove ruleAA

* feat: add checkValidSrc

* wip: init crossIn in checkValid()

* wip: add vm.Verify for *bc.CrossChainInput

* feat: skip gas for CrossChainInput

* refactor: clean up

* fix: fix protobuf

* fix: fix validate tx

* update (t *TxInput) AssetAmount()

* add (t *TxInput) Amount()

* update

* clean

* wip: types/txinputs.go

* feat: draft types.TxInput

* fix: fix test

* clean

* fix outputID

* init assetDefinition

* add read/write AssetDefinition

* fix the merge issue