Support for fat-arrow `=>` using Function.bind
Allow using #external as expressions -- fixes #15
Merge master changes
Merge pull request #31 from drslump/external-as-expression

Allow using #external as expressions
Merge pull request #30 from drslump/fat-arrow

Support for fat-arrow `=>` using Function.bind
Reimplemented => with a captured variable, and changed tests because it seems that global != this at the top level.