0.6.0

CHANGES:

• Add a Docker backend for Windows and Linux jobs.
  (@MisterDA #127 #75, reviewed by @talex5 and @tmcgilchrist)

• Add FreeBSD sandbox backend using jail(8)
  (@dustanddreams #156 #174, reviewed by @tmcgilchrist, @MisterDA, and @mtelvers)

• Add Macos ZFS sandbox (@mtelvers #164, reviewed by @tmcgilchrist)

• Support XFS store (@mtelvers #170, reviewed by @tmcgilchrist)

• Search for bash rather than assume it lies in /bin (@dustanddreams #159, reviewed by @tmcgilchrist)

• Prune builds one at a time up to the limit (@mtelvers #157)

• Specify upper bound on number of items in the store (@mtelvers #158, reviewed by @MisterDA)

• Fix case where BTRFS is not fully allocated (@mtelvers #162)

• Avoid pruning parent cache objects (@mtelvers #176, reviewed by @tmcgilchrist)