Runscript 2.0 Beta 2

And this is why I started calling these betas now. I want to use it, and using it has let me more easily catch how I want it to feel.

Changes and fixes since 2.0-beta.1

• Phase flags -b -r -t now actually work; I forgot to link them up before.
• The default target is now the first target in the file (perhaps syntax could be introduced later to override this), instead of [:run] being an implied header at the start of the file.
• You can now pass -1 or --old-format to get a best-effort parsing of the runscript 1.3.0 format. In particular, includes and global/pre-global scripts are unsupported; the old phase system is coerced into the new one (b!, b => "build"; br, r, r! => "run"); and commands are parsed with conch_parser in the same way as the new format.
• The -1 flag and the current file being executed are preserved through the recursion boundary (at least, on unix systems)