Empty file should not be treated as missing
An empty file (i.e., file contents == "") was being treated as missing when trying to compile it. This is undesirable, and should not cause an error at all, as the empty string is a valid Roy program. The cause of this was the empty string being interpreted as falsy in `if(!source)`. This patch refactors the getFileContents function to fix this. It also tidies a few things, e.g. removing unused variables.
Update underscore to 1.5.2, change test after _.max to -Infinity.
Add some basic type parser tests
Multi line repl
…t. Fixes #44