VM improvements, tests + bugfixes (#61)

* changed vm commands to match more of the standard

* fixed Uint16 jmp bug in VM

* moved test to vm + fixed numnotequal bug

* fixed broken tests

* moved compiler tests to vm tests

* added basic for support + inc and dec stmts

* bumped version

pkg/vm/stack.go

@@ -61,7 +61,7 @@ func (e *Element) Prev() *Element {
 // Will panic if the assertion failed which will be catched by the VM.
 func (e *Element) BigInt() *big.Int {
 	switch t := e.value.(type) {
-	case *bigIntegerItem:
+	case *BigIntegerItem:
 		return t.value
 	default:
 		b := t.Value().([]uint8)
@@ -99,6 +99,13 @@ func NewStack(n string) *Stack {
 	return s
 }
 
+// Clear will clear all elements on the stack and set its length to 0.
+func (s *Stack) Clear() {
+	s.top.next = &s.top
+	s.top.prev = &s.top
+	s.len = 0
+}
+
 // Len return the number of elements that are on the stack.
 func (s *Stack) Len() int {
 	return s.len