Fix PATH export recompilation hell (FINALLY!)
Add utils/io.lua for creating io.exists function if it doesn't already
exist.
Add boolean return values to all targets to determine if they went right
or wrong.
				On target error, the entire process is halted.

Fix build target not building. Now builds using the bundles .spm/bin/tup
executable.
Fix configure target not configuring. Now configures using primitive
methods.
Remove duplicate git.clone function from pull target. Pull target
already depends on clone target which includes (and executes) the
git.clone function.