Added description of occ.
add documentation to deprecated functions in PETSc::MPI::Vector
Merge pull request #242 from tjhei/petsc_documentation_fixes

add documentation to deprecated functions in PETSc::MPI::Vector
Merge pull request #241 from luca-heltai/occ-entry

Added description of occ.
Add OpenCASCADE installation instructions.
Merge pull request #243 from bangerth/add-occ-blurb

Add OpenCASCADE installation instructions.