e0 is created only if there are null vectors in the algebra, and the 3d
and 2d basis groups have been rearranged to compensate in the changed
ordering in the basis blade array.
Currently only PGA(3) is supported, but that's because the parser is
rather simple (recursive descent with a lame lexer), but it works well
enough for playing with geometric algebra without having to recompile
every time.
