Add license
Parsing basic predicates

only two types:

* variable equality defined using

  `some_var is 'expected'`

* set inclusion defined using

  `some_var in {set of things}`
Add a few more negative test cases in parser spec
Add named predicate parsing
Simple rule parsing
Parsing of nested rules

Credit due to Nigel Thorne for his solution for parsing indented data
structures with parslet given via stackoverflow[1].

[1] http://stackoverflow.com/a/16563186/800501