Clean up only created device or directories by the process

[nak3]

device: clean up only created device or directories by the process

This patches introduces a map to hold devices or directories which created by the process
for cleaning up them when Close is called.

Fixes #7

[mdlayher]

Seems Iike the map should exist as a struct field on Device instead of as a package level variable.

[nak3]

Thank you. Yes, I agree. I updated.