Replaces the existing Africa with a revised, identically sized one.
Revisions include addition of navigable rivers allowing the interior to
have access to trade.
Chnages to the json file to take the number of Nation bots from 5 to 36.
Should help prevent so much early game blobbing on this map.
Also updated the map loader to now run on every single map (in the
`maps` array).
Also now maps are loaded concurrently (run every promise at the same
time and wait that they are all finished). As the functions are CPU
bound and not IO bound running concurrently doesn't change much right
now but it can if we use more promise in the function loadTerrainMap
then things will get faster.
APuddle210