Toro et. al. 1997 GMPE as needed for the 2008 NSHMP-US model
Frankel et al. 1996 GMPE
Campbell 2003 GMPE for 2008 US hazard model
changed class name from FrankelEtAl1996NSHMP to FrankelEtAl1996NSHMP2008
removed unneeded import
changed class name from ToroEtAl1997NSHMP to ToroEtAl1997NSHMP2008
Merge pull request #171 from monellid/Campbell2003NSHMP

Campbell 2003 GMPE for 2008 US hazard model
Merge pull request #169 from monellid/toro1997_nshmp

Toro et. al. 1997 GMPE as needed for the 2008 NSHMP-US model
set rupture and distance context params in test without calling setattr
Merge pull request #170 from monellid/FrankelEtAl1996

Frankel et al. 1996 GMPE
AB2006 - 140 bar
atkinson & boore 2006 (200 bar stress drop)
moved common methods to utils module
added tests for utility methods
updated doc
fix typo
removed unneeded import
silva et al. 2002 for US 2008 model
Merge pull request #172 from monellid/ab2006_nshmp

Implement Atkinson and Boore 2006 GMPE for 2008 US model
Merge branch 'master' into silva_2002