make parser embeddable in code with other parser (yy->gmsh_yy)
more work on headers
fixed lots of gcc warnings

fix position of BoundaryLayerPoints

- implemented all missing 2nd order representations
- removed unused member functions in GFace + cleaned up GFace::point

curvature control is ok
divide and conquer algo has been cleaned up

Plane surfaces are now recognized and the
usual gmsh "cross" is drawn correctly

prepare for extrusion