Fix subtraction on the Log type.

Fixes #9
Merge pull request #10 from glguy/fix-subtraction

Fix subtraction on the Log type.
version bump
noted that we fixed subtraction into the changelog
Merge pull request #8 from EldradUlt/master

Fixed Subtraction
0.9.2 bump and CHANGELOG
support generic-deriving 1.7
Revert "Fix subtraction on the Log type."

This reverts commit 7f7d4921fb47bdc55a1cf1d71cf1234aac9c1864.
version bump
0.9.3 mea culpa in the CHANGELOG