Add support for C++/Rust templates/generics

[nitnelave]

AFAIU, it should be a simple matter of adding "<>" as "parenthesis-like" objects: it could pose problems with expressions with comparisons, though:

template <typename T, typename P>
void do_the_thing(int i) {
  do_the_thing_impl(i, i > 3);
}

If the cursor is on "typename P" and I press "da,", I expect that the text ", typename P" is deleted. But if it's on the "i" in "i > 3", "da," should delete ", i > 3" (and not just ", i " as if ">" was the end of the argument).