compound junctions

Major changes:

• Additional "distances" parameter added to match_pts_to_graph() to return geodesic distance to point of edge intersection.
• Fixed major bug in centrality calculations on graphs with duplicated edges (#186).
• Added new vignette with instructions on parallel thread control
• New function, dodgr_deduplicate_graph() to reduce duplicated edges and insert minimal distances/times (#187)
• weight_streetnet function now returns standard graphs even when turn_penalty = TRUE; compound junctions are calculated within each function (#190).

Minor changes:

• Walking cost function in networks with elevation improved (#124)
• Fixed weight_streetnet.sc to respect "bicycle" and "foot" tags for those weighting profiles (#189)