schema/hazard:

Moved `PlanarSurface` to `general.xsd` and re-use it in the SES schema.
schema/hazard/general.xsd:

Removed some trailing whitespace.
examples:

Reordered planar surface points to consistent with OpenQuake conventions.

Order is now: top left, top right, bottom left, bottom right.
examples:

Consistent ordering of corner points in planar surface elements (top left, top
right, bottom right, bottom left).
tests/hazard/writers_test:

Fixed ordering of planar surface points to match schema.
schema/hazard/general.xsd:

PlanarSurface now requires that points are ordered top left, top right, bottom
right, bottom left.
hazard/writers:

Fixed a PEP8 indentation issue.
hazard/writers:

Updated SESXMLWriter to support writing multi planar surface ruptures.
tests/hazard/writers_test:

Updated SES XML serialization tests to exercise multi-surface writing.
Changed ordering of planar surface points:

I had made some false corrections before. The ordering should be:
- top left
- top right
- bottom left
- bottom right
hazard/writers:

Updated some comments.
Merge pull request #84 from larsbutler/ses-multi-surface-rupture

SES multi surface rupture support

[r=matley] [f=*1144225,1144207]