Resolves: #920

I used the sample input to test against, and added a few validations that I also tested locally to ensure they worked.

templ example(x int) {
	switch x {
        case 0:
            fallthrough
        case 1:
            <p>hey</p>
    }
}

@example(0) now properly prints <p>hey</p>

The following things were included as well

• Validation that fallthrough doesn't appear as any other statement than the last one in a case statement
• Validation that fallthrough isn't used on the final case statement
• Validation that fallthrough isn't follow by anything other than a newline.

This is my first contribution to the project though, so please comment away if anything can be improved!