Merge pull request #43 from doug-martin/master

v0.1.6
Merge pull request #47 from doug-martin/master

#0.1.7 / 2013-06-25
Merge pull request #48 from doug-martin/master

#0.1.8 / 2013-08-14
Added support for unary negation
Added support for setting precedence using parentheses
Fixed examples after testing
Fixed logging mistake
* Fix fact retraction in the not node
Fix for issue #50
Fix for issue #53