Bump version number to 0.5.6.0
Add Ross Paterson to 2014 copyright statement

He wrote the first draft of the new `fromList` code.
Merge pull request #97 from treeowl/add-credit

Add Ross Paterson to 2014 copyright statement
Fix warnings.

In getNodes, pass (a, [a]) instead of an [a] which we know is nonempty.
This way we do not have to create void pattern-match case for empty
list.

Also use STRICT_x_OF_y macros instead of `seq`-ing in every
pattern-match case.
Nuke include/Typeable.h, create include/containers.h instead.

The "Typeable.h" collides with the header of same name in base.

The new "containers.h" is now used in every Haskell source.
It contains more stuff used across the containers codebase:
- INSTANCE_TYPEABLE[0-2] (was in Typeable.h)
- include MachDeps on __GLASGOW_HASKELL__ to define WORD_SIZE_IN_BITS
- define STRICT_x_OF_y macros
- define MIN_VERSION_base if not defined by cabal (during cabal-less build)
Add the include dir also to tests.

This worked with Typeable because Typeable from `base` instead of
`containers` was used.
Disable coercion tests for the time being.
Remove circular `toList` definition.

When writing this, I assumed we have explicit `toList` as we have in
other containers. We do not have `toList`, and even if we did, the code
would not compile, as the two `toList`s (ours and `Foldable`) would
collide.
Import only used class methods of Foldable.

On GHC 7.8, the Foldable class contains also null and length, which
conflicts with Data.Sequence{null,length}.
It is perfectly fine to import class methods...

...without specifying the class, see Haskell 2010 5.2.1.
That allows us to get rid of some conditional includes.

Nevetheless, we still conditionally include foldr', as we do not
use it for base <4.8.
Add forgotten foldMap to the imports.

The foldMap is in Prelude on base 4.8, that is why I missed it.
Bump version number to 0.5.6.1