Closes #388

Functions with properties are now supported (including via declaration merging with namespaces). This is done by wrapping the function definition in a "callable" table (using the __call metamethod).

Example:

function foo(s: string) { return s; }
foo.bar = "bar";

local foo = setmetatable(
    {},
    {__call = function(____, self, s)
        return s
    end}
)
foo.bar = "bar"

Additionally, this fixes #1174 and fixes #1179 as I needed those working for tests.