Add to_str() for HashMaps, and some basic tests as well.
Removed test_hashmap() for the time, being. All tests pass with make check.
All tests, including newly added test_hashmap() pass. The empty Hash Table doesn't need to be mutable.
Remove extra space between key and value.

1. Extra space removed.
2. Using acc.push_str() instead of str::push_str
3. Update test to reflect representation change.
Add str representation for HashSet.
Add test: test_hashset()
Use acc.push_str() instead of str::push_str(..)

Also added some whitespace to enhance readabilty.
Fix errors in test_hashset().

All tests now pass.
Add use declaration for container::Set

All tests pass now.
Make Float::classify matching more clear for f64 and f32
Created utility uninhabited type

In this commit I added a useful utility type, named Void, that encapsulates the
doable but annoying job of creating an uninhabited type. As well, a function on
that type, named absurd, was created which is useful for ignoring the result of
matching on that type. No unit tests were created because it is not possible to
create an instance of this type to test the usage of.

This type is useful because it is like NonCopyable in that it can be used to
create a type with special characteristics without special bloat. For instance,
instead of typing pub struct PhantomType { priv contents : () } for each void
type one may want to use one can simply type pub struct PhantomType (Void);.
This type make such special cases much easier to write.
update: vec.rs each2_mut
add: testsuite vec.rs each2_mut function