Progress Tracker: Feature Requests and Bug Reports

[NStefan002]

• [x] #6 (by @Davidyz)
• [x] Clear Screenkey after some time (by u/evergreengt on Reddit)
• [x] Add a debug option (by @Makaze)
• [x] Key grouping (by u/OkDifference646 on Reddit)
• [x] Option to display <leader> (by u/OkDifference646 on Reddit)
• [x] Make window persistent - cannot be closed by something like <c-w>o (by u/yetAnotherOfMe on Reddit)
• [x] Screenkey should always be on the visible tab (by u/yetAnotherOfMe on Reddit)
• [x] 'send to back' / 'send to front' kind of behavior (closes #5)
• [x] more window options (by @biozz)
• [x] #19 (by @cvigilv)
• [x] #25 (by u/hallettj on Reddit)
• [x] #26 (by @nicolas-goudry)
• [x] #31 (by @nhattruongNeoVim)
• [x] #38 (by @miron2363)
• [x] #36 (by @XavierChanth)
• [x] #37 (by @frvnzj)
• [x] #43 (by @konosubakonoakua )
• [ ] #47 (by @arielherself)

If you'd like to suggest any features, feel free to open up a feature request.