Vim mode

Each of these keys don't work as intended at certain points in the document:

Normal Mode
- [ ] o -- On the last line of the document
- [ ] A -- On the last line of the document
- [x] $ -- On the last line of the document
- [x] O -- On the first line of the document
- [x] I -- (Capital 'i') On the first line of the document
- [x] 0 -- (Zero) On the first line of the document
-- From my investigation: In Vim.hs, these keys use the functions startOfLine and endOfLine. Both these functions search for a newline character which I assume is missing at the start and end of the document.

Insert Mode
- [ ] Backspace -- At the start of any line will Backspace will delete any text to the right of the cursor, then once the line is empty will cause the cursor to disappear on that line and delete the line beneath it.

- [ ] x -- Will delete empty lines.

Start by reading Vim.hs and inspect the startOfLine and endOfLine paths used by the listed Normal Mode keys. Check the Insert Mode handling for Backspace and x at line boundaries and empty lines; done means each unchecked behavior matches the described Vim behavior without regressing the checked cases.

Written by the indexing model from the issue text.