Logging command

[roboguy13]

It would be nice to have a logging function logStr :: String -> Shell () (hopefully with a better name than that) which would print something to stdout.

At the moment, hermit-shell displays the results of each step it performs and we might be able to use that as an advantage if we have a way of printing out comments to go along with those steps. For example, saying which lemma it is about to apply. You could also name different sections of the transformation in a script. This would make it quite a bit easier to follow along with each step as it runs a script.

[andygill]

I've added Shell to the LiftIO class. So you can now do

liftIO $ print "Hello"

in the Shell. Though, after a day of debugging, we do need much better debugging and tracing capabilities.