This PR brings everything up to what is spec'd out here: #250 (comment)

• non-static class/interface methods and function properties (lambdas) are given a context parameter
• static methods/lambdas and stand-alone functions have no context parameter
• errors are thrown for attempts to assign methods to non-methods and vice-versa
• stand-alone functions can be given a context by explicitly adding a 'this' parameter
• methods can be declared without a context by explicitly declaring a 'this: void' parameter

A few notes:

• NoContext decorator has been removed
• bind/call/apply currently throw errors when called with non-methods. Are there any good reasons to support this?
• Custom constructor functions are expected to be non-methods. If that needs to be supported, it might need to be an option in the decorator.

Current edge cases:

interface Func<T> {
    (this: T, s: string): string;
}
let fn: Func<void> = foo.method; // Should Error

Right now, Func is detected as having context when it shouldn't. I need to figure out how to resolve the generic parameter when checking assignments.

interface A {
    method(s: string): string;
}
interface B {
    method(this: void, s: string): string;
}
declare let a: A;
let b: B = a; // Should Error

Assigning to interfaces allows the check to be bypassed and calling the method on 'b' will incorrectly use the dot syntax. This should be solvable by recursively checking assignments to interface types, but this is complex and will likely add quite a lot of overhead. Need to think on this one...