Add create dir, delete dir/file

[vnghia]

This PR adds create dir, delete dir/file

[mihaimaruseac]

Minor nit is just a question.

[mihaimaruseac]

Nit: Can we ensure that object always ends with a /?

[vnghia]

Sorry I dont understand what you mean. MaybeAppendSlach will ensure object will end with a '/'

[mihaimaruseac]

I meant object is always produced by other functions. Can we ensure that those functions add the trailing slash?

Basically, from the point of view of a caller to ParseGCSPath, object either always has the trailing / or not but not something in between. Otherwise, you always have to write code that uses both ParseGCSPath and MaybeAppendSlash.

[vnghia]

I think we could force object always has the trailing / or not in ParseGCSPath but it causes many unwanted behaviors.

In the local filesystem, we have a function mkdir to create directory and the directory name can have / or not, it does not matter.

But with gcs filesystem, we have to create an empty object with the name ends with / so Google Cloud Console could display it as a directory.

If we force object does not have / at the end, Google Cloud Console will display that object as a empty object.
If we force object has / at the end, Google Cloud Console will display everything as a directory ( even the object's size is bigger than 0 ).

[mihaimaruseac]

Ok, then let's leave it as it is