New {{cursor}} placeholder for prompts

[Entaigner]

Text manipulation around the text cursor

1. {{cursor}}

• Returns the text cursors current line

2. {{cursor:2:5}}

• Returns the text from... 'cursor line-2 at the start of the line' to 'cursor line+5 at the end of the line'

3. {{cursor:1:1:'[SOME_MARKER]'}}

• Like 2. but inserts [SOME_MARKER] at text cursor position

Important:

• When text is selected the cursor position is always at the end of selection
• Only one {{cursor}} marker may be included in any prompt

Why: https://huggingface.co/stabilityai/stable-code-3b#run-with-fill-in-middle-fim-%E2%9A%A1%EF%B8%8F

[Entaigner]

The pull request might've been a little rash but i got lost in the moment whilst testing a model.

My implementation lacks a comfortable integration into the rest of the project.

Maybe {{selection_with_marker}} to allow the placement of a marker somewhere in the selection. Or keep {{cursor:1:1:'[SOME_MARKER]'}} but without the line deltas {{cursor:'[SOME_MARKER]'}} and select after. Haven't figured it out.

Anyway, thanks for the awesome project.