Explore options other than `attach()` for `autos`

[nicholas-masel]

An autos() feature is that you can attach multiple environments to the search path, and the order they are attached takes care of which function to use if there are multiple with the same name.

Could we use {conflicted} here to explicitly pick the functions and add them to search?

Steps:

1. Read envsetup config file for autos.
2. Identify conflicts.
3. Use conflicted to set the preferred functions in the search path.

Step 2 needs some more thought.

Originally posted by @nicholas-masel in #75

[nicholas-masel]

@mstackhouse I'm now just thinking we write everything to global and just shim source to check what already exists in global before adding objects. So source will not overwrite objects and will provide a message, similar to the library masking messaging, that says what was added from the sourced script to global and what was not since it already existed in global.

I have a good example of this now, but I'll add a little testing and put in a PR for review/comment.

[nicholas-masel]

Closed by #82