Added support for directory visiblity

[sjadema]

Added visibility when creating directories
Added a namespace for the unit tests
Added a test case for the new behaviour

Fixes #4

[sjadema]

@twistor Bump! I really need this PR for my project <3

[twistor]

What is the use case? Flysystem doesn't support visibility for lots of filesystems, so I'm not sure if this is a good idea.

[sjadema]

I need an in-memory FS with directory support for https://github.com/twistor/flysystem-stream-wrapper. I've created an issue about a more defensive approach to the visibility Furthermore, the in-memory adapter is capable of directory visiblity (as it's capable of file visibility) so it wouldn't harm to add it imho.

[rulatir]

Is there any hope for this to ever be merged? If this comment has a chance of catching @twistor's attention - @twistor, do you still maintain flysystem-stream-wrapper?

[rulatir]

B
U
M
P

[Crell]

Here's the issue: Often, the in-memory filesystem is used in tests for a system that will be using a non-memory filesystem in production. That means if the production filesystem ever wants to use is_dir(), you now cannot run tests, because the memory filesystem doesn't support it at present. This PR should, I think, resolve that issue, which is currently a blocker for elazar/flystream#9.