Examine the naming of frame, low_level_data and curr_data

[asgibson]

The naming of these items has been brought into question during the review of #58.
Frame has apparently been renamed to low_level_data, but not everywhere. It will require some research as to where the monikers should be applied. i.e., frame is also referred to as 'frames' in certain locations, which makes a simple find/replace change to low_level_data not feasible (frame -> low_level_data, but frames -> low_level_datas). The curr_data moniker is included here because in the vehicle_rep the frame is merged into curr_data.

[asgibson]

This is most likely related/same as #52