Release Splice version 3.0.0-alpha.27.
Release Splice version 3.0.0-alpha.27.

 * Upgrade `riffle` to `2.0.0-alpha.40`. Closes #186.
 * Upgrade `b-tree` to `2.0.0-alpha.63`. Closes #185.

Closes #187.

bigeasy/splice,bigeasy/splice