renamed BaseSurface to BaseQuadrilateralSurface, created new abstract class BaseSurface and new MultiSurface
more correct implementation of get_rx_distance method
added more tests for distance calculation with 1D Meshes
fixed bug in mesh.get_joyner_boore_distance - now the algorithm works also when 2D Mesh objects are passed
fixed bug in planar.get_joyner_boore_distance - now it works also with 2D Mesh objects
Merge branch 'master' of github.com:gem/oq-hazardlib into multi-rectangle-surface
updated init files
removed wrong comment
fixed documentation
Merge branch 'master' of github.com:gem/oq-hazardlib into multi-rectangle-surface
Merge pull request #107 from monellid/multi-rectangle-surface

Multi Surface