Intellij-rust: Add postfix templates for Result/Option wrapping

[panstromek]

When you write functions that return Result or Option, it's very common to write out full expression first and then wrap it in Ok($expr) and alike. It would be great to have postfix templates for these operations.

Specifically:

• $expr.ok<caret> expand to Ok($expr)
• $expr.err<caret> expand to Err($expr)
• $expr.some<caret> expand to Some($expr)
• $expr.none<caret> expand to None($expr)

[Undin]

$expr.none expand to None($expr)

Probably, did you mean something else? Option::None doesn't have any fields

[panstromek]

@Undin Oh, right, I didn't think about it 😄 nevermind that case then.

[panstromek]

This seems like a pretty easy task, so I am gonna give it a shot. I wanted to start contrubuting at some point anyway ;)