[Tolk] Get rid of ~tilda with mutate and self methods

This is a very big change.
If FunC has `.methods()` and `~methods()`, Tolk has only dot,
one and only way to call a `.method()`.
A method may mutate an object, or may not.
It's a behavioral and semantic difference from FunC.

- `cs.loadInt(32)` modifies a slice and returns an integer
- `b.storeInt(x, 32)` modifies a builder
- `b = b.storeInt()` also works, since it not only modifies, but returns
- chained methods also work, they return `self`
- everything works exactly as expected, similar to JS
- no runtime overhead, exactly same Fift instructions
- custom methods are created with ease
- tilda `~` does not exist in Tolk at all

tolk-tester/tests/a6_1.tolk

@@ -5,12 +5,18 @@ fun main(a: int, b: int, c: int, d: int, e: int, f: int): (int, int) {
   return (Dx / D, Dy / D);
 }
 
+@method_id(101)
+fun testDivMod(x: int, y: int) {
+  return [divMod(x, y), modDiv(x, y), mulDivMod(x, y, 10)];
+}
+
 /**
-    method_id | in            | out
-@testcase | 0  | 1 1 1 -1 10 6 | 8 2
-@testcase | 0 | 817 -31 624 -241 132272 272276 | 132 -788
-@testcase | 0 | -886 562 498 -212 -36452 -68958 | -505 -861
-@testcase | 0 | 448 -433 -444 792 150012 -356232 | -218 -572
-@testcase | 0 | -40 -821 433 -734 -721629 -741724 | -206 889
-@testcase | 0 | -261 -98 -494 868 -166153 733738 | 263 995
+    method_id   | in            | out
+@testcase | 0   | 1 1 1 -1 10 6 | 8 2
+@testcase | 0   | 817 -31 624 -241 132272 272276 | 132 -788
+@testcase | 0   | -886 562 498 -212 -36452 -68958 | -505 -861
+@testcase | 0   | 448 -433 -444 792 150012 -356232 | -218 -572
+@testcase | 0   | -40 -821 433 -734 -721629 -741724 | -206 889
+@testcase | 0   | -261 -98 -494 868 -166153 733738 | 263 995
+@testcase | 101 | 112 3 | [ 37 1 1 37 33 6 ]
 */