Add multimap! macro

[dfaust]

Add a multimap! macro plus some minor fixes.

[thejpster]

Thank you so much for this. I'm so happy someone else found this crate useful enough to send a PR!

Could you briefly explain the macro - I can't quite work out what's going on, especially as it's recursive. Could you also change the test to verify the macro had actually created the multimap you expect it to. I wonder if we should implement PartialEq - it might make those macro tests easier as we could check for equality with a hand built multimap.

Thanks!

[dfaust]

The macro is pretty much copied from https://github.com/bluss/maplit, so to be honest I'm not 100% sure what it does myself :). Unfortunately I couldn't find anything about calculating the length of the macro arguments. The recursion is due to the macro being re-used to perform multiple calculation steps using the prefixes @single and @count.
The last two arms are the entry points. The first has a trailing comma, the second doesn't. In case of a trailing comma it is stripped away and the macro is called again.
At first the length of the arguments is calculated by calling the macro with the @count prefix.
The length is then used to allocate enough memory.
After that all arguments are inserted into the map.

Could you also change the test to verify the macro had actually created the multimap you expect it to

sure

Implementing PartialEq would make sense Debug probably as well (needed for assert!).

[thejpster]

Right, gotcha. Thanks.

[thejpster]

Superb.

[thejpster]

Submitted 1.1.0.