[Tolk] Rewrite lexer, spaces are not mandatory anymore

A new lexer is noticeably faster and memory efficient
(although splitting a file to tokens is negligible in a whole pipeline).

But the purpose of rewriting lexer was not just to speed up,
but to allow writing code without spaces:
`2+2` is now 4, not a valid identifier as earlier.

The variety of symbols allowed in identifier has greatly reduced
and is now similar to other languages.

SrcLocation became 8 bytes on stack everywhere.

Command-line flags were also reworked:
- the input for Tolk compiler is only a single file now, it's parsed, and parsing continues while new #include are resolved
- flags like -A -P and so on are no more needed, actually

tolk/unify-types.cpp

@@ -354,12 +354,6 @@ std::ostream& operator<<(std::ostream& os, const UnifyError& ue) {
   return os;
 }
 
-std::string UnifyError::message() const {
-  std::ostringstream os;
-  print_message(os);
-  return os.str();
-}
-
 void check_width_compat(TypeExpr* te1, TypeExpr* te2) {
   if (te1->minw > te2->maxw || te2->minw > te1->maxw) {
     std::ostringstream os{"cannot unify types of widths ", std::ios_base::ate};