This update fixes some issues with the number of simulation ticks spent on imports.
-`from file import` now costs 1 tick.
-`import file` is still free.
-Reading from a module like `y = file.x` is now free as long as the variable `file` has been assigned by an import statement. This is analogous to functions being free as long as they have been directly assigned by a def statement, and prevents exploits that abuse the dynamic nature of modules to do completely free computations.
-Writing to modules like `file.x = y` now costs the same as reading from them.
-`def` and `import` statements inside an `if`, `while` or `for` block no longer make the functions/modules they create free, because this could also be used to do free computations.
-Fixed importing into local scope.