DEV 1247: Add a new map generator interface (#71)

* reorganize code

* first draft of map generator interfaces

* add explicit random interface to board helpers

* implement standard map

* rename Generator to GameMap

* allow initializing snakes separately from placing them

* add random number generator to Settings

* updates to GameMap interface

* add helpers for creating and updating BoardState with maps

standard_test.go

@@ -15,7 +15,7 @@ func TestStandardRulesetInterface(t *testing.T) {
 func TestSanity(t *testing.T) {
 	r := StandardRuleset{}
 
-	state, err := CreateDefaultBoardState(0, 0, []string{})
+	state, err := CreateDefaultBoardState(MaxRand, 0, 0, []string{})
 	require.NoError(t, err)
 	require.NotNil(t, state)