Add "Bash extension" to allow Paisley to be run as a shell interpreter

[ZacharyWesterman]

This will require:

• REPL
• filesystem support
• allow reading command return value
• allow reading stderr
• allow running any command in the system PATH, or locally
• more??

Basically this will be a superset of Paisley, with more syntax that the Plasma version doesn't have.

[ZacharyWesterman]

I think this goes outside the scope of Paisley. It was never meant to run as a shell interpreter, and adding all these features requires significant overhead