Feature/20 monorepo support

[copdsUcn]

Hi!
A few days ago, when I was trying to use a monorepo, I encountered the problem that in your repo was already mentioned and documented as issue #20.

I found the idea of recursively searching node_modules/.bin directories a bit wild. Forty's idea of allowing a list of commands albeit quite sexy.

I took the liberty of sending you a PR that implements this function. It looks like a lot of code, but it's just a bunch of helper functions and the proper remodeling of the add-node-modules-path interactive function.
Additionally a short paragraph in the README.md as well as ert tests.

Of course, the implementation is backwards compatible; it is still possible to use the default value of add-node-modules-path-command or override it with a single command.

Due to the fact that with several commands some commands can work well, but others don't, I had to adjust the reporting. Directories that could be added to exec-path are reported using (message ...). Commands that failed are reported as warnings in the Warnings buffer.

Maybe you are interested in the extension. otherwise just ignore :)

best regards from austria,
Max

[codesuki]

Great contribution! Thank you! Just a small nit: what about making the commands a list instead of a comma separated string?

[copdsUcn]

This would definitely be the cleaner solution.
I will soon provide an update of the PR that is also backward compatible regarding the according defcustom :type

[copdsUcn]

Hi!
I updated the PR. Multiple commands are now specified as list instead of a comma-separated string.
The defcustom :type was changed from string to (repeat string). To ensure backward compatibility, a custom :set function was added as well to convert a string value to a single-element list of this value. This way, users with an already existing customization in their config are able to open the customization UI and see their string value properly converted and displayed.

[codesuki]

Very cool! Thanks a lot for working on this!