update to work with post alpha nightly

[dcampbell24]

Conrod is not currently building due to breaking changes released with the alpha.

[dcampbell24]

The macros need to be updated due to the breaking changes, but I am having trouble figuring out what the proper changes are.

One breaking change is the requirement for a separator between the multiplicative matcher fragment and the fragment before it per RFC 550. My proposal for fixing this is to change for example

($context:ident, $cb:ty $(, $t:ident)*) => ...

to

($context:ident, $cb:ty, $($t:ident),*) => ...

requiring an extra comma at some call sites.

Another breaking change is caused by the changes to closures. I can't figure out how to update impl_callable to handle the new syntax.

Any suggestions?

[dcampbell24]

This is a duplicate of #239 closing.

[dcampbell24]

I am going to rebase #239 and then merge it. So this will serve to track that.

[dcampbell24]

Decided a new PR is not really necessary.