`inim -i -s=file` to enter interactive inim session instead of exiting upon completion
ipython3 --help:
```
If you  specify the option `-i` before the filename, it will enter an interactive
    IPython session after running the script, rather than exiting. Files ending
    in .py will be treated as normal Python, but files ending in .ipy can
    contain special IPython syntax (magic commands, shell expansions, etc.).
```

as ipython, inim should not exit inim shell upon completion of the script `file`, regardless of success/failure

- [ ] NOTE: the `.ipy` point is interesting, we could have a .inim with same intent; would be useful eg for testing inim; that point is low priority though

