Use YAML file to keep .RProfile as light as possible

[moodymudskipper]

If think it's more elegant, and we can keep the active binding abstractions out of the .RProfile, and the comment blocks will go away with it.

We just need in the .RProfile:

# setting up package to use 'dir', set the behavior in 'dir.yml'
setHook(packageEvent("dir.example", "onLoad"), function(...) dir::setup())

dir::setup() will fetch all the input it needs from the YAML file and call add()

Another benefit is we can update the YAML file and load_all() to apply our changes, no need to restart the package.