hazard/writers, __init__:

Updated hazard writers to be able to write to either a file-like object
or simply a file path.
__init__:

Added a comment to the Output class.
risk/writers:

Updated risk writers to be able to write to either a file-like object
or simply a file path.
__init__, hazard/writers, risk/writers:

Renamed the Output class to NRMLFile. We can use this for the readers
as well, so this is a better name for input/output files.
__init__:

The default mode for NRMLFile changed from 'w' to 'r'. This makes more
sense, since Python's built-in `open` behaves this way.
Merge pull request #101 from larsbutler/better-file-handling

NRML parsers/writers should be able to accept either file paths or file-like objects

[r=matley] [f=1202131]
Fixed an XML example file
Implemented a StreamingXMLWriter
Merge pull request #102 from gem/streaming-xml-writer

Implemented a StreamingXMLWriter