Remove the separator characters construct

Now, grammars can handle whitespace by making it another ubiquitous
token, like comments.

For now, this has the side effect of whitespace being included in the
tree that precedes it. This was already an issue for other ubiquitous
tokens though, so it needs to be fixed anyway.

src/runtime/stack.h

@@ -25,6 +25,7 @@ void ts_stack_push(TSStack *stack, TSStateId state, TSTree *node);
 TSStateId ts_stack_top_state(const TSStack *stack);
 TSTree *ts_stack_top_node(const TSStack *stack);
 size_t ts_stack_right_position(const TSStack *stack);
+TSTree **ts_stack_pop_extras(TSStack *, size_t *);
 
 #define TS_STACK_FROM_TOP(stack, entry, index)               \
   size_t index = stack.size - 1;                             \