Attempt to fix issue 43

[Skgland]

maps error for all remove_dir_all calls where the result is not ignored (all but one) to the added Custom error type to also display the directory path

EDIT: also do this for file removals

[pietroalbini]

Thanks for working on this! Left some feedback.

[shepmaster]

This may be reimplementing https://crates.io/crates/fs-err

[Skgland]

Did't know about fs-err until now. Though that wouldn't work for remove_dir_all as this project is not using std::fs::remove_dir_all, probably because of rust-lang/rust#29497.
So that wrapper of the two would still be necessary.

[Skgland]

Though it might be reasonable to also get better errors for other Filesystem operations using fs-err only leaving remove_dir_all like this.

[Skgland]

Opened PR #47 to expand on this using fs-err for all Filesystem operations where possible.

[pietroalbini]

I feel like this approach is better than #47: bringing another dependency just for this is not really needed.

Thanks for working on the PRs! Merging.