[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.

crypto/fift/lib/Asm.fif

@@ -1589,6 +1589,9 @@ forget @proclist  forget @proccnt
 { }END> b> } : }END>c
 { }END>c <s } : }END>s
 
+// This is the way how FunC assigns method_id for reserved functions.
+// Note, that Tolk entrypoints have other names (`onInternalMessage`, etc.),
+// but method_id is assigned not by Fift, but by Tolk code generation.
 0 constant recv_internal
 -1 constant recv_external
 -2 constant run_ticktock