- Add new mappings for character insertion:
- `[count]<Leader>I(char)` - Insert a character at the beginning of the line
- `[count]<Leader>A(char)` - Insert a character at the end of the line
- Update insertion commands to reflect new functionalities:
- `:InsertCharBegin (count) [char]` - Insert a character at the beginning of the line
- `:InsertCharEnd (count) [char]` - Insert a character at the end of the line
- Introduce an option for a static cursor during insertion actions.
- Update README.md with instructions and notes for vim-repeat (`.`) support
- Update doc/singlechar.txt: add requirements, usage, and tips for vim-repeat, including installation and dot-repeat behavior
