Added functionality to automatically deal with gzip files instead of requiring user to specify a custom "open" function.
This change is mostly backwards compatible since the user can still specify an open function to call.
The non-backwards compatible changes are due to changing raw "open()" calls to "self.open()", and adding "self.mode" to the self.open calls.
Merge branch 'master' of github.com:nevermindewe/blaze