Update compiler (#22)

* refactor to use ast.Walk for recursive converting
* added lots of test cases
* added a new way to handle jump labels
* function calls with multiple arguments
* binary expression (LOR LAND)
* struct types + method receives
* cleaner opcode dumps, side by side diff for debugging test cases

pkg/vm/compiler/tests/assign_test.go

@@ -0,0 +1,31 @@
+package compiler_test
+
+var assignTestCases = []testCase{
+	{
+		"chain define",
+		`
+		package foo
+		func Main() int {
+			x := 4
+			y := x
+			z := y
+			foo := z
+			bar := foo
+			return bar
+		}
+		`,
+		"56c56b546c766b00527ac46c766b00c36c766b51527ac46c766b51c36c766b52527ac46c766b52c36c766b53527ac46c766b53c36c766b54527ac46203006c766b54c3616c7566",
+	},
+	{
+		"simple assign",
+		`
+		package foo
+		func Main() int {
+			x := 4
+			x = 8
+			return x
+		}
+		`,
+		"53c56b546c766b00527ac4586c766b00527ac46203006c766b00c3616c7566",
+	},
+}