WIP: towards detecting arbitrary URLs and make them clickable

[christianparpart]

Closes #1078 Closes #421

this PR is of course not even remotely usable yet, but it's here to track the progress.

Checklist

Checklist for implementing this could look like:

• [x] regex_dfa: integrate DFA regular expression engine from klex project
• [x] regex_dfa: adapt to get all compiler diagnostics green
• [x] regex_dfa: integrate tests
• [ ] auto-detect URL patterns in the grid buffer
• [ ] vim mode: gx to open the URI (or file) underneath the cursor position
• [ ] vim mode: ]x to jump to next and [x to jump to previous URI (or file) in screen's grid buffer
• [ ] allow customising how to detect what an URI is via a regex through the config file (profile).
• [ ] visually differentiate matches (just like search/click matches) to make cycling through them and quickly identifying them visually more appealing
• [ ] support matching URLs as well as local filepaths, into a single DFA
• [ ] support caching the compiled DFA onto disk (with a checksum to ensure it wasn't tempered with) and reload that on next startup to avoid slowing down startup-times.