Release Paxos 19.0.0-alpha.2.
Release Paxos 19.0.0-alpha.2.

 * Tidy `.npmignore`. Closes #452.
 * Sort `.gitignore`. Closes #451.
 * Remove `/.proof.out` from `.gitignore`. Closes #450.
 * Remove Monotonic dependency. Closes #449.

Closes #453.

bigeasy/paxos,bigeasy/paxos