Left action

[rrbruner]

We had trouble getting the Steenrod algebra to act on the left, but found that it does
work on the right. (!) This is not a real right action though: (x * a ) * b computes bax,
whereas x*(a*b) computes abx.

[kvwoerden]

In the branch koen-leftrightmult (that everybody is welcome to work on) I attempted to make the Steenrod algebra act on the left by implementing the coercion framework.

It sort of works I think, but it definitely needs more work because it breaks some things now. In particular, line 26 from the sample session from Mike's thesis doesn't work anymore (which uses submodule(), which I think is broken now.)