* print an error if one comes back from running compiled binary
* rework the code a little bit and make sure mage -version prints to stdout
* export CmdRan and use it so we only log an error of not being able to run the magefile
* Helpers galore
This commit adds helper functions that should be commonly needed
by many magefiles. It includes command execution handlers as well
as error handlers.
This commit also removes the only two non-stdlib dependencies in
the codebase. Since mage will likely be vendored into a repo,
it would be nice to avoid cluttering the vendor directory with
dependencies that are only for the build script.
