Force overtype (rather than insert) key behaviour, block newline entry, delete and backspace

[pachpict]

(This is all part of a project to use Micro to create a 'typewriter' mode for the Canute Console Braille display, referenced here: #2973.)

Could I have some advice about how to force micro to do several things related to key entry?

1. Start micro with the assumption that the insert key has been pressed so it starts overwriting? (I'm not bothered either way if the user can 'flip' this by pressing the insert key or if its locked into overtype mode).
2. Block newline entry with the enter key, delete or backspace. Alternatively could remap behaviour so enter is mapped to replicate down arrow behaviour, delete to right arrow, backspace to left arrow.

I appreciate that there will remain other ways of the user forcing text inserted (pasting), or deleting (using ctrl+k) and so on. That's OK for now, this is a prototype.

Thank you for your help, Micro continues to open up wonderful opportunities with the Canute display.

Ed