Improves Warning messaging

[ghost]

Improves on the original warning.warn message (for when an envfile wasn't found) by including the search path used for a given file.

[rconradharris]

Looks useful.

Think an additional function for this is probably overkill, just adding a list of paths we've traversed to read_envfile should be good enough.

[ghost]

Thanks for saying that it looks useful and for quickly responding to the PR (👍 ).

I think the last commit is what you had in mind, but let me know if I misunderstood and I can modify it.

[ghost]

It is worth noting that the change to only use a list in that fashion means that the UserWarning will contain all failed path lookups (i.e. read_envfile('a'); read_envfile('b') will show warnings on 'b' that contain paths from 'a'). Let me know if you want me to write in the "only show warnings for filename" behavior.

[MichaelCurrie]

@rconradharris are you still maintaining this repo? The last commit is 7 years ago. Thanks