VM and compiler update (#63)

* renamed test folders and fixed bug where wrong jump labels would be exectuted for rewrite.

* Added support for Osize (len(string)) and factored out the array tests

* Added current instruction number to VM prompt if program is loaded.

* added support for unary expressions.

* updated README of and sorted the help commands

* updated readme of the compiler

* bumped version -> 0.39.0

pkg/vm/tests/numeric_test.go

@@ -0,0 +1,18 @@
+package vm_test
+
+import "math/big"
+
+var numericTestCases = []testCase{
+	{
+		"add",
+		`
+		package foo
+		func Main() int {
+			x := 2
+			y := 4
+			return x + y
+		}
+		`,
+		big.NewInt(6),
+	},
+}