wk 0.8.0

• Added wkb_to_hex() (@anthonynorth, #183).
• Implemented vctrs::vec_proxy_equal() for wkb() vctrs
  (@anthonynorth, #183).
• Fixed sfc_writer(), which had returned NULL for some inputs
  (e.g., via wk_collection()) (@anthonynorth, #182, #186).
• Added wk_clockwise() and wk_counterclockwise() to re-wind polygon rings
  (@anthonynorth, #188).
• New replacement-function mode for wk_coords<-() for in-place modification
  of coordinates (@mdsumner, #187).
• New function wk_trans_explicit() migrated from crs2crs (@mdsumner, #187).