Use single-precision floats in remollIO

[wdconinc]

Is your feature request related to a problem? Please describe.
Remoll output files become quite big quickly. We currently store 238 bytes per hit. A lot of this is in the double values for positions and momentums, both in global and local coordinate systems. Speed of analysis of the output files is typically linear in the file size, so it would speed that up too.

Describe the solution you'd like
We could shift to using float for positions and momentums, but maintain double for the energy, momentum, and mass.

Describe alternatives you've considered
We could do nothing. This would be perfectly adequate as well.

[wdconinc]

@cipriangal @rahmans1