compiler,runtime: implement maps for arbitrary keys

This implementation simply casts types without special support to an
interface, to make the implementation simpler and possibly reducing the
code size too. It will likely be slower than the canonical Go
implementation though (which builds special compare and hash functions
at compile time).

testdata/map.txt

@@ -54,5 +54,20 @@ true false 0
 42
 4321
 5555
+itfMap[3]: 0
+itfMap[3.14]: 3
+itfMap[8]: 8
+itfMap[uint8(8)]: 80
+itfMap["eight"]: 800
+itfMap[[2]int{5, 2}]: 52
+itfMap[true]: 1
+itfMap[8]: 0
+floatMap[42]: 84
+floatMap[43]: 0
+floatMap[42]: 0
+structMap[{"tau", 6.28}]: 5
+structMap[{"Tau", 6.28}]: 0
+structMap[{"tau", 3.14}]: 0
+structMap[{"tau", 6.28}]: 0
 tested preallocated map
 tested growing of a map