Improve readability of WITH expressions

[pombredanne]

Expressions such as "Foo WITH Bar OR Baz" are not super readable because the operator precedence is not something super intuitive.
It would be great to have the option to render an expression this way: "(Foo WITH Bar) OR Baz"

[pombredanne]

This has been merged but keeping it open until we have a changelog

[steven-esser]

#48 has been merged, and license-expression now has a changelog. Closing this.