Run rsync with project as working directory

[enykeev]

When you start to follow the idea proposed in #38 and try to use shell parameter to set path to identity file, there is no way to set it relative to the project directory.

This PR makes rsync execute with project directory as cwd so every relative path is now resolved against it. You can still use absolute paths or ~ shortcut.

[enykeev]

Personally, I'm planning to use it with vagrant. Instead of modifying .ssh/config for every project I have, I can just copy-paste .sync-config.cson:

remote:
  host: "localhost"
  user: "vagrant"
  path: "/tmp/some"
behaviour:
  uploadOnSave: true
  syncDownOnOpen: true
  forgetConsole: false
  autoHideConsole: true
  alwaysSyncAll: false
option:
  shell: 'ssh -p 2202 -i .vagrant/machines/default/virtualbox/private_key'
  deleteFiles: false
  exclude: [
    ".sync-config.cson"
    ".git"
    "node_modules"
    "tmp"
    "vendor"
  ]

[ayurmedia]

FYI: i pulled your new feature to:
ayurmedia#4

https://github.com/ayurmedia/atom-sync-cygwin

[ayurmedia]

FYI: i reverted the pull request on atom-sync-cygwin, because it caused side effects and bugs in the context menu for sync. see details here:

ayurmedia#7

[enykeev]

Cleaning up my Pull Requests tab