Add vinbt support

When using `clicraft edit <file>`, edit <file> using vinbt when it
makes sense to do so.
Change `clicraft explore` usage

Having to feed mcexplore options to this script isn't very useful,
so make it accept the size in blocks and optionally the center
coordinates instead.

For more control over the mcexplore command that gets launched,
users can invoke mcexplore directly or write their own action
with `clicraft edit`.
Add dimdir() function

Add a function for looking up the directory a dimension lives in
from its name.

This function was taken from the prune.sh example script, so remove
it from there as well.
Fix typo in defaults.sh
Tweak list()

I'm not sure if this function ever worked properly, but hopefully
it should be better now.
Add wickedwhich() function

Useful for searching for utilities that might be installed outside
of the system PATH.
Use wickedwhich()
Fix dimdir() function

This got lost in the commit that introduced it.
Handle dimdir() and serverprop() failures better

Check for nonzero return values on these functions and handle
accordingly.
Add `clicraft sh` action

Useful for debugging.
Make pregen.sh args match explore.sh usage

Make the interface to these two scripts as close as possible to
avoid confusion.
Tweak explore.sh

* Don't overestimate map size, despite the integer math
* RADIUS isn't actually a radius, so rename it to SIZE
* Fix typo: explore2 -> explore