Improve get-position to properly handle block comments and multi-line braces

[nickyhajal]

Here's a pull request that should resolve #14 as well as #10. It also detects flow type import type definitions, and places other imports above those (so the order is external imports -> local imports -> type imports)

To do this it adds a few methods to get-position:

isComment, isTypeDefinition and isInBracketOrComment.

There's some added complexity in the main get-position function to track the context that the current line is part of (if it is within a block comment or a bracket), plus some additional logic to handle those conditions.

I think I've handled most of the edge cases but please test and let me know if it needs any further improvements!