Use MonadHandler constraint

[felixSchl]

This removes the hard dependency on running in IO and instead requires to run in any m that has a MonadHandler instance. Fixes #2.

[geraldus]

@felixSchl Thanks!
I never seen several => going one after another. Is it another way to write several constraints without parentheses and commas?

[felixSchl]

Yeah both ways works, but this one stacks nicely. Do you want me to change it?

[felixSchl]

I'll change it because i had another look over the code and I see you use the other style in other places

[geraldus]

Merged, thanks @felixSchl !

I'll bump version and push it to Hackage soon.

[skinner33]

I'm rather unsure if this is necessary. I have to admit that I do not have a test for a yesod subsite, yet IO is not needed anywhere. A simple Monad m typeclass is sufficient. Especially as I was unable to add MonadHandler IO into my applications (in the end, mkYesodDispatch throws some template errors).

I'm opening another PR (#4) to change this, it would be awesome if you could verify if this also works for subsites.

[geraldus]

@felixSchl can you please check if proposed Monad constraint work for subsites?