added assert
documentation fix
Merge branch 'master' of https://github.com/gem/oq-hazardlib into fix-1154024
added another check in the complex fault
fixed error propagation
Merge pull request #111 from matley/fix-1154024

Restrict ComplexFaultSourceSurface to not pathological cases
si and midorikawa 1999 gmpe
fixed bug in std calculation for interface gmpe
implemented Si and Midorikawa 1999 tests
tests for si & midorikawa 1999
Merge pull request #113 from monellid/si_midorikawa

Si and Midorikawa 1999
Merge branch 'master' into rob-hazardlib