Support for import aliasing

[smuuf]

Currently import std.types will always import module types into variable types, or import std.term.colors: Fg will always import name Fg from module std.term.colors into variable Fg.

What we want to allow are these:

>>> import std.types as lol_std_types

... or:

>>> import import std.term.colors: Fg as colors_fg

... or even:

>>> import import std.term.colors: Fg as colors_fg, Bg as colors_bg