Updates meshing function for the full annulus
- 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()