Allow blocks without else.

[clarfonthey]

It doesn't seem immediately obvious from the documentation that you can't do a block without an else branch, so, I added that functionality.

[alexcrichton]

Out of curiosity, do you have a use case for this? This was originally intentional because I'd consider it bad practice to not have a fallback

[clarfonthey]

I mean, I make pretty extensive use of it in len-trait and it seems excessive to have to add else {} everywhere.

[alexcrichton]

Ah ok, that seems reasonable!

[clarfonthey]

Would you be willing to push another version to crates.io for this?

[alexcrichton]

Sure, published