Consider regenerating completions on bashly generate

[DannyBen]

Right now, the only way to regenerate the bash completions function is by rerunning bashly add comp function.

The reasons it is like this are:

1. Different users will choose different places to integrate these completions
2. There is no place in the config file to specify things like "and also regenerate completions"

Although it seems like a high level of effort for the time being to change this, from user perspective, it is most definitely needed.

It would be nice if bashly generate is smart enough to know how completions were added, and redo the same thing.

[DannyBen]

Implemented in the master branch, but only on completions that were added using bashly add comp function.

Once the version is released, users already having such completions need to re-add them once with --force and from this point on, running bashly generate --upgrade will also regenerate the function.