Fix lexer

[uk-ar]

Sometime lexer returns different tokens between swift-smie--backward-token and swift-smie--forward-token. The examples is below.

• When "foo:", forward-token returns "foo:" but backward-token returns "foo" and ":".
• When "typealias", forward-token returns "typealias" but backward-token returns "typeali" and "as".

So I add test code to check swift-smie--backward-token and swift-smie--forward-token. And fix those lexer. How about this?

[uk-ar]

Hi @ap4y ! Thank you for reviewing. I fixed (require cl)

[ap4y]

Thanks!

[uk-ar]

Thanks for merging :smile: !