Rename neighbor list and options

[ceriottm]

With the introduction of a flag for "strict" neighbor lists, it makes sense to reconsider a bit how flags are set and interpreted. It would make sense to rename:

• Neighbor list -> Pair list (since now this is not supposed to be strict "neighbors"
• full -> half (the natural behavior is that all pairs are listed, and "half" is opt-in
• maybe change the name of "strict" if we can find something more telling