Release Riffle version 2.0.0-alpha.27.
Release Riffle version 2.0.0-alpha.27.

 * Use new Trampoline class. Closes #166.
 * Upgrade `b-tree` to `2.0.0-alpha.46`. Closes #165.
 * Upgrade `destructible` to `7.0.0-alpha.11`. Closes #164.
 * Remove caret pin from alpha dependencies. Closes #163.

Closes #167.

bigeasy/riffle,bigeasy/riffle