first implementation of CharacteristicSource
Merge branch 'master' of github.com:gem/oq-hazardlib into characteristic_source
implemented tests for characteristic source
pep8 fixes
updated doc file, and init
Minimal fix to get_available_gsims
Merge pull request #108 from monellid/characteristic_source

Characteristic source
Merge pull request #109 from gem/fix_get_available_gsims

Minimal fix to get_available_gsims
geo, source:

Renamed `CharacteristicSource` to `CharacteristicFaultSource`.
tests/source/characteristic_test:

Renamed `CharacteristicSource` to `CharacteristicFaultSource`.
source/characteristic:

Minor pep8 fix.
tests/sources/characteristic_test:

Minor pep8 fix.
Merge pull request #110 from larsbutler/char-fault-source

Rename CharacteristicSource to CharacteristicFaultSource

[r=trivial]