hazard/writers:

Added `SourceModelXMLWriter`. It still needs documentation, though.
hazard/parsers:

Fixed a comment.
tests/hazard/writers_test:

Added `SourceModelXMLWriterTestCase`.
tests/hazard/writers_test:

PEP8 whitespace fix.
hazard/writers:

Added missing docstrings to `SourceModelXMLWriter`.
hazard/writers:

Better docstrings for `SourceModelXMLWriter`.
tests/hazard/writers_test:

Cleanup temporary test files in `SourceModelXMLWriterTestCase`.
hazard/writers:

Handle the optional source model name properly when writing a source
model.
models:

Updated copyright date.
models:

Added `attrib` to MFD model classes.
models:

Added `SeismicSource` base class, with common `attrib`.
models:

Added `attrib` to `NodalPlane` and `HypocentralDepth`.
hazard/writers:

Use model class `attrib` for writing source models.
Merge pull request #90 from larsbutler/src-model-xml-writer

Source model XML writer

[r=micheles] [f=*1096867]