Allow users to run in thermal noise only mode

[jsdillon]

By passing --eor None, one can run without any eor model, producing thermal noise only errors. Among other things, this allows one to go up to high k, beyond the limits of the power spectrum interpolator. In this case, both errs and T_errs are identical.

I also fixed a number of numpy issues by explicitly casting results of round to ints.

(Also, I fixed the tabbing in one section. Who tabs with 3 spaces?)