Add a way to define functions with copying closures

[evhub]

Should have a way to create a function that copies the locals() in the calling function at the time of creation rather than simply grabbing a reference to them. For lambdas, will probably only be for statement lambdas.

[evhub]

After a bunch of testing, it looks like we should be able to get this to work by compiling (exact syntax still TBD)

def outer_func():
    funcs = []
    for x in range(10):
        closure def inner_func():
            return x
        funcs.append(inner_func)
    return funcs

to something like

def outer_func():
    funcs = []
    for x in range(10):
        _inner_func_vars = globals().copy() | locals().copy()
        exec("""def inner_func():
    return x""", _inner_func_vars)
        inner_func = _inner_func_vars["inner_func"]
        funcs.append(inner_func)
    return funcs

[evhub]

Some syntax options:

closure def inner_func() = x
closed def inner_func() = x
bind def inner_func() = x
copyclosure def inner_func() = x

[evhub]

Syntax that we're going with for this is

copyclosure def inner_func() = x