Fixes a problem with the flagging of tangential edges where the
annulus is "glued" together; re-inserted edges were all markes as inner.
Removes old version of MeshAnnulus() that had CRISSCROSS hardcoded.
Updates MeshGenTest to test all four meshing flavours.
Introduces hollowFlag enum in MeshInfo class for setting in a mesh generator
flagInnerBoundary, flagInterior, flagOuterBoundary for closed and hollow
domains such as the full annulus and the thick spherical shell. MeshAnnulus()
now used these.
Extends documentation.
Also fixes clipping of CRISSCROSS and CROSS picture for MeshRectangle()