need to move the key stuff to a new branch and finish it on its own probably

k and N not confusing variable names at all...

Lots of fields left incorrectly populated but at least the erasure encoding is
working so we can probably read (without verification) real shares now.

Add a Binary instance to deserialize from and serialize to the canonical byte representation

Closes #4

See merge request !3

Specifically, this will build our new `make-keypairs` executable.

Add a representation of the share data

See merge request !2

Read Tahoe-LAFS-generated bytes, decode into a Share, re-encoded to the same
bytes.

Just a round-trip-through Binary test for now

* We can always interpret the IV so represent it using the IV type instead of
  as bytes.

* We cannot interpret the private key without its decryption key so represent
  its encrypted form as bytes.

Take tahoe-chk as a dependency because it can already represent some of the
fields of an SDMF share.  Also, a crypto library for key representations.

Fix a typo in the cabal file that passed with only a warning before.

Configuration for CI

See merge request !1