match points

Breaking changes:

• match_pts_to_graph() renamed to match_pts_to_verts()
• New match_pts_to_graph() function matches to graph edges, using nearest perpendicular intersection (issue #103)

Major changes:

• dodgr_paths pairwise calculation shifted to C++, thanks to @dcooley

Minor changes:

• Fix dodgr_flowmap to work on both sf and sc streetnets.
• Reformat code using https://github.com/ropensci-review-tools/spaceout
• Minor bug fix matching from/to args of dodgr_flows_aggregate()
• Bug fix when submitting contracted graphs to flow fns
• Change default value in all dodgr_flows_ functions from contract = FALSE to contract = TRUE