CRAN version 0.2.0

Major changes:

• Lots of intermediate processes now executed and cached as background processes (via callr package).
• new dodgr_cache_off function added to suppress primary caching, for cases where immediate usage is critical.
• dodgr_contract_graph returns the contracted graph only, instead of former version which return list of graph and edge_map (the edge_map is cached and re-loaded when needed for graph uncontraction).

Minor changes:

• 'turn_angle' parameter of weight_streetnet renamed to turn_penalty
• Test coverage now complete (100%)

• Update internal hampi data to remove factor columns

• Fix some bugs in max speed calculations for weight_streetnet

• Fix bug with polygonal bbox in dodgr_streetnet()