[IMP-dev] Moving algebra to doubles

As was mentioned before, it is probably a good idea to move all the storage and computations in the algebra module to use "doubles" in order to improve numerical robustness. IMP::Float would stay as "float" for now. Probably the cleanest way to do this is to replace all "Float" with "double" in the existing code. This appears to work without problems.

If no one objects, I'll submit the patch soon.