Functions for operating on Maps from C (#725)

new API functions for maps:
wrenSetSlotNewMap
wrenGetMapCount
wrenGetMapContainsKey
wrenGetMapValue
wrenSetMapValue
wrenRemoveMapValue

test/api/maps.wren

@@ -0,0 +1,68 @@
+class ForeignClass {
+  construct new() {}
+}
+
+class Maps {
+  foreign static newMap()
+  foreign static insert()
+  foreign static contains(map, key)
+  foreign static contains()
+  foreign static containsFalse()
+  foreign static count()
+  foreign static count(map)
+  foreign static remove(map)
+  foreign static invalidInsert(obj)
+}
+
+// map new + get/set API
+
+var map = Maps.newMap()
+System.print(map is Map) // expect: true
+System.print(map.count) // expect: 0
+
+var data = Maps.insert()
+System.print(data["England"]) // expect: London
+System.print(data["Empty"])   // expect: []
+System.print(data[1.0])       // expect: 42
+System.print(data[false])     // expect: true
+System.print(data[null])      // expect: null
+
+// remove API
+
+var removed = Maps.remove({ "key":"value", "other":"data" })
+System.print(removed) // expect: value
+
+var removedNone = Maps.remove({})
+System.print(removedNone) // expect: null
+
+// count API
+
+var countMap = { "key":"value", "other":"data", 4:"number key" }
+System.print(Maps.count(countMap)) // expect: 3
+Maps.remove(countMap) //remove using API
+System.print(Maps.count(countMap)) // expect: 2
+countMap.remove("other") //remove wren side
+System.print(Maps.count(countMap)) // expect: 1
+
+var countAPI = Maps.count()
+System.print(countAPI) // expect: 5
+
+//contains key API
+
+var containsMap = { "key":"value", "other":"data", 4:"number key" }
+System.print(Maps.contains(containsMap, "key")) // expect: true
+System.print(Maps.contains(containsMap, "fake")) // expect: false
+System.print(Maps.contains(containsMap, "other")) // expect: true
+
+Maps.remove(containsMap) //remove using API
+System.print(Maps.contains(containsMap, "key")) // expect: false
+
+containsMap.remove("other") //remove wren side
+System.print(Maps.contains(containsMap, "other")) // expect: false
+
+System.print(Maps.contains()) // expect: true
+System.print(Maps.containsFalse()) // expect: false
+
+//
+
+Maps.invalidInsert(ForeignClass.new()) // expect runtime error: Key must be a value type.