* Add checkpoint list generation scripts
* Limit the checkpoint block data size
* Limit the checkpoint height gap
* Add Mainnet and Testnet checkpoint lists
* Parse hard-coded checkpoint lists
The lists were generated using the following limits:
- 256 MB spacing, based on block byte size, and
- 2000 blocks.
* Flatten consensus::verify::* to consensus::*
* Move consensus::*::tests into their own files
* Move CheckpointList into its own file
* Move Progress and Target into a types module
QueuedBlock and QueuedBlockList can stay in checkpoint.rs, because
they are tightly coupled to CheckpointVerifier.
teor
Alfredo Garcia