* New method type: extension methods. Extension methods enable you
to "add" methods to existing types without modifying the original type.
Extension methods are a special kind of static method, but they are
called as if they were instance methods on the extended type.
Extension methods are identified by "Usage: Extension" and the
type they extend is determined by their first argument contract.
Thus such methods must have at lease one parameter.
* New type-level keyword "Import" which can be either list or
scalar that specifies type names which extensions methods
should be imported into class context and thus become available
to type members.
Change-Id: If757327857376ac66784acd4bd29471e6f28b612
73f798da57