* WIP: Update for testing with Merge fixturenet.
* Switch channel to take a *Transaction rather than []byte. This allows us to access the TX fields (eg, for logging) throughout its lifecycle.
* Tweak message
* Add code to check for TXs being put into blocks.
* 0 == unlimited
* Use -1, not 0, for unlimited.
* golang 1.19
* Read contract from file.
