Release B-tree version 2.0.0-alpha.6.
Release B-tree version 2.0.0-alpha.6.

title: Release B-tree version 2.0.0-alpha.6.
label: release

 * Fix name of MIN and MAX symbols. See #572.
 * Not vivifying left page in utilities. Closes #578.

Closes #579.

bigeasy/strata,bigeasy/strata