Pypred

* Python3 support
* Added support for `==` operator
* Permit unicode in predicates
* Support for case insensitive operators
* Tested on python 2.7, 3.4, 3.5 & pypy
* SHA: ccc76fb

* Improve the optimization of LiteralSet by making sets as small as possible,
and avoiding branches on low density sets.
* SHA: e8dbdb4

* Added Literal Set support. This allows for sane contains with a literal
collection of Literal, Number, or Constant values.
* SHA: 5a2d4f1

* Fixed optimizer to handle missing cases
* Internal change to use EvalContext instead of passing around multiple objects
* .analyze() now return the EvalContext instead of a dict
* Duplicate expressions are cached to avoid wasted re-evaluations. This allows
expressions with low selectivity to still avoid being re-evaluated, even though
they are not in a branch.
* Export ast.Undefined from the pypred package, since it is generally useful
for writing custom resolvers.
* SHA: 7d44ae4

* NegateOperator provides failure information
* SHA: dd79246

* Optimizations for memory utilization
* Input predicates are no longer deep copied (bug fix)
* Fix bug with compiling an empty set
* SHA: f645507