Fixing initial session state

Fixing the lack of this._sessions initialisation when no file exists.
Fixing the broken call to this.all() at the end of this.get()
Optimising the stringifying of an empty object to the static string
Removing the console output from this.set()
Merge pull request #3 from Krylik/empty-file-fixes

Fixing initial session state
Merge pull request #1 from darul75/master

Merging upstream