Stop using the shell to run commands

[myyk]

This prevents RCE with $(...) syntax, and makes the regex escaping functions unnecessary, and the code slightly cleaner.

Fixes #287

Manually tested on Ubuntu running locally.

Setup:

Before:

After:

[suspicious-pineapple]

why is this not merged? seems like a huge security flaw, especially when you have untrusted user input in the prompt and the output.