add Gauss quadrature on triangles
add FeTRI3
add tests for FeTRI3
fix compiling errors in MSVC
Merge pull request #403 from norihiro-w/fix-fe_errors

fix compiling errors in MSVC
Merge pull request #388 from norihiro-w/add-fe-tri

Add FE type TRI3
Small fix for the ninja build system.

See http://docs.opengeosys.org/docs/devguide/advanced/build-with-ninja
fix a compiling error in MSVC
Merge pull request #404 from norihiro-w/fix-fetri-error-msvc

Fix a compiling error in MSVC.
First version of RefineLayeredMeshInZDirection.
Split prism and tet elements.
splitElement() does not work for tets.
Calculate volume within the mesh for different element types.