Runscript 2.0 Beta 3

I want to stop calling this 2.0, really. It makes it seem like a 3.0 could be coming at some point.

Changes and fixes since last release:

• You can now source basic shell script files.
• When recursively running, the default target is the one currently being executed, instead of the runscript's own default.
• Now exits early when a command fails (did it not do that before?)
• #3 No longer panics when running an empty target. (There's still plenty of potential panics in the code, though. Don't you worry)
• General printing and formatting improvements