Elfs

- fix infinite loop if replace-str is in replacement arguments
- changed flags for adding commands to spellbook

- bug fixes for tab-completion
- add support for dynamic tab-completion in scripts, the same way it was implemented here for fish
- for example, use the following json to add dynamic tab-completion to a second elfs.py to run from elfs (`elfs elfs.py [args]`)
- `[{"command":["python3", "elfs.py", "--_completion", "(commandline)"]}]`

- New feature: dynamic tab-completion