BJF 1993 GMPE for Western Canada Model
added test for LowerLimit case and created doc file
Merge branch 'master' of github.com:gem/oq-hazardlib into bjf93
Merge pull request #151 from monellid/bjf93

Implement Boore, Joyner and Fumal 1993 GMPE for 2010 Western Canada Model
Merge branch 'master' of github.com:gem/oq-hazardlib into ab1995
improved comment