Add basic idempotent file operations module

This commit adds a basic module with a few idempotent file
operations:

- mkdir
- chown
- chmod

Mkdir composes/accepts ownership/group ownership/mode options
so as to conveniently set the state of the directory that got made:

mkdir("/foo/bar", {
  'owner': 'elliot',
  'group': 'framed',
  'mode': '02775'
})
Merge pull request #15 from elliot42/master

Add basic idempotent file operations module