Allow substring comparisons (#15)

* Support substring comparions for 'contains' and 'ncontains'

* Fix some comments

* Add benchmarks for string contains

add regular expression comparator

remove ability to create engines without json

make use of maps to speed up oneof and noneof

Merge pull request #11 from huttotw/feature/performance

feature/performance

Merge pull request #10 from acoulter1/master

Add noneOf comparator

Merge pull request #7 from huttotw/feature/ncontains

feature/ncontains

fix some copy pasta

drop support for all types other than float64 and string

Merge pull request #5 from huttotw/fix/float64

fix/float64