changed _pd_meas.time_of_flight and _pd_meas.step_count_time from Integer to Real

[rowlesmr]

from #60

The only things that are still integers are:

• _pd_meas.counts_background, counts_container, counts_monitor, and counts_total.
• _pd_meas.number_of_points
• _pd_pref_orient_March_Dollase.hkl, index_h, index_k, index_l
• _pd_pref_orient_sphericalharmonics.y_i, y_ij, y_j
• _pd_proc.number_of_points