Switch/case documentation gotcha

"Unintuitively", Haxe cases are absolutely strict, so this can bite:
```
switch (x) {
case 1:
case 2: trace('1 or 2'); // nope, never fall through
}
```
And the documentation doesn't explain how to declare a case matching several values - though it is explained deeper in the pattern matching documentation.

Still it's a bit confusing: is it `case 1, 2:` or `case 1 | 2:`?

It would be nice for beginners to add something.

Read the switch/case documentation alongside the pattern matching documentation referenced in the issue. Clarify that cases do not fall through and document the syntax for matching several values, with an example that beginners can verify against Haxe's existing behavior.

Written by the indexing model from the issue text.