Merge the topic/mi-methods-attributes branch.

Merge the topic/mi-methods-attributes branch.

This moves several pieces of functionality into new Mixins so that they can
more easily be reused by Moose, in particular by Moose::Meta::Role and
Moose::Meta::Role::Attribute.

Squashed commit of the following:

commit c871d3eac7cc21ad8dbe6169100feb0514dc4837
Author: Dave Rolsky <autarch@urth.org>
Date:   Sun Jan 3 10:44:17 2010 -0600

    Add minimal pod to mixin classes, add versions, and update pod spelling & coverage tests

commit 3c688b21fd9c4187a8f8b81bec3ff570367d9c2e
Author: Dave Rolsky <autarch@urth.org>
Date:   Sun Jan 3 00:05:47 2010 -0600

    Changes for next version

commit 9e3ca77b02a577f17dad4312b057778b30531b43
Author: Dave Rolsky <autarch@urth.org>
Date:   Mon Dec 28 11:14:24 2009 -0600

    Mixins no longer inherit from CMOP::Object.

    They now inherit from CMOP::Mixin, which just provides a ->meta method.

commit 84dd9b9ac630c5f4f05fda1c92475622bd1d1b59
Author: Dave Rolsky <autarch@urth.org>
Date:   Mon Dec 28 11:06:53 2009 -0600

    rename AttributeBase -> AttributeCore

commit 41d62121a64393345bbdddb71a461521db397132
Author: Dave Rolsky <autarch@urth.org>
Date:   Sat Dec 26 13:11:10 2009 -0600

    only require that attributes implement CMOP::Mixin::AttributeBase to add them to a thing which has attrs

commit 2611f98e2b56d77be2974b624519ceb3260c4e20
Author: Dave Rolsky <autarch@urth.org>
Date:   Fri Dec 25 19:52:52 2009 -0600

    move core meta-attribute attributes to a mixin class for benefit of role attributes

commit 30bf0c82239247a48a464619231ab931c80d2f67
Author: Dave Rolsky <autarch@urth.org>
Date:   Fri Dec 25 10:57:52 2009 -0600

    Rename HasMethod & HasAttributes as Class::MOP::Mixin::...

commit 5e31ca05f9630c567662f23263fa8722cd301444
Merge: 8860f0f 3aad1e2
Author: Dave Rolsky <autarch@urth.org>
Date:   Fri Dec 25 10:39:48 2009 -0600

    Merge branch 'master' into topic/mi-methods-attributes

commit 8860f0f14413d44f94eee530852edd254200a46c
Author: Dave Rolsky <autarch@urth.org>
Date:   Fri Dec 25 10:38:07 2009 -0600

    Refine HasAttributes a bit more so that it only contains the minimum shared behavior between CMOP::Class and Moose::Meta::Role

commit 2d413af5a93064413d7b005150623ab1d70bb25e
Author: Dave Rolsky <autarch@urth.org>
Date:   Thu Dec 17 11:22:56 2009 -0600

    Don't call meta instance related methods unconditionally in HasAttributes.

    Move get_all_attributes back to CMOP::Class, since it only makes sense for
    things with inheritance.

commit b71bd1cded366fe62f4a44471908dd57a8686077
Author: Dave Rolsky <autarch@urth.org>
Date:   Wed Dec 16 14:24:14 2009 -0600

    Moved attribute management to CMOP::HasAttributes.

    Next step is to make Moose::Meta::Role work inherit from this class.

commit e3e651fb972d8c9c1cf82574b53dcc8cadfb717a
Author: Dave Rolsky <autarch@urth.org>
Date:   Wed Dec 16 11:52:38 2009 -0600

    Move having methods to a new superclass - Class::MOP::HasMethods