GitLab

Interactive PoRep will split the existing seal operation into a
two-step flow. In the first step, the pre-commit operation will persist
some artifacts to a per-sector directory (a subdirectory of the
sector cache root-dir) for the commit operation to load.

Closes #2 

- sector id is now a uint64
- generate_post accepts faults instead of producing them
- generate_post produces a single proof instead of a concatenation of proofs
- verify_post accepts a single proof

feat(stub piece expiry UTC seconds argument)

feat(add basic build)