Recursively load .envs up to root

[daboross]

One thing this crate was missing before, and is still missing, is the ability to load multiple cascading .env files.

For example, if I have the following in project/.env:

X=1
Y=2

And the following in project/subdir/.env:

Y=5

It would be ideal if running dotenv::dotenv() in project/subdir/ would load

X=1
Y=5

---

I think one of the hardest parts of this is the API design, though, especially with specifying manual filenames (or directory names for cascading).

If you'd be willing to support this, I would recommend iterating on solutions before committing to 1.0.

Recursively loading files up to the root is definitely something I will look into. With manual file specification my instinct is that if a custom filename is provided then that will be the filename that is searched for recursively up through the directories since that is the behavior today with single-file merge.