[Tolk] v0.6 syntax: fun, import, var, types on the right, etc.

Lots of changes, actually. Most noticeable are:
- traditional //comments
- #include -> import
- a rule "import what you use"
- ~ found -> !found (for -1/0)
- null() -> null
- is_null?(v) -> v == null
- throw is a keyword
- catch with swapped arguments
- throw_if, throw_unless -> assert
- do until -> do while
- elseif -> else if
- drop ifnot, elseifnot
- drop rarely used operators

A testing framework also appears here. All tests existed earlier,
but due to significant syntax changes, their history is useless.

tolk-tester/tests/inline_loops.tolk

@@ -0,0 +1,48 @@
+global g: int;
+
+@inline
+fun foo_repeat() {
+  g = 1;
+  repeat(5) {
+    g *= 2;
+  }
+}
+
+@inline
+fun foo_until(): int {
+  g = 1;
+  var i: int = 0;
+  do {
+    g *= 2;
+    i += 1;
+  } while (i < 8);
+  return i;
+}
+
+@inline
+fun foo_while(): int {
+  g = 1;
+  var i: int = 0;
+  while (i < 10) {
+    g *= 2;
+    i += 1;
+  }
+  return i;
+}
+
+fun main() {
+  foo_repeat();
+  var x: int = g;
+  foo_until();
+  var y: int = g;
+  foo_while();
+  var z: int = g;
+  return (x, y, z);
+}
+
+/**
+   method_id | in | out
+@testcase | 0 |    | 32 256 1024
+
+@code_hash 102749806552989901976653997041637095139193406161777448419603700344770997608788
+*/