distinguishing between macros and special expressions
Environment.contains should search all scopes
initialising an environment should take all its scopes as an argument
Fixing RPython build errors

Since we don't have any Macro instances yet, RPython's typecheck doesn't
know that Macro instances would have .call() defined.

%r also isn't supported by RPython.
discussing treating true, false and null as literals

I'm still unsure about this. `lambda` is currently just a variable, so
we shoudn't make the printed representation be the raw source, or we get
the same problem if the user sets the `lambda` variable.
implementing a basic `lambda`
implementing zip() to keep RPython happy, and grouping RPython
conveniences into almost_python.py
Ensure lambda variables do not leak, but allow closure variables to be updated
correcting docs that incorrectly refer to macros
documenting trifle lisp conventions
documenting how to build the interpreter
documenting `lambda`
updating status
adding some examples of how scopes work
adding a unit test for comments
documenting comments
evaluating nothing should return `null`