[states] add some documentation for extension wrapping

[states] update qimport code so it doesn't fails on qimport without -r

mention plan for hook in the documentation

[obsolete] published changeset can't be obsoleted states extension is now required. A warning message is emitted when obsoleting a published changeset.

[obsolete] update docstring

[obsolete] remove useless code.

[obsolete] rationalize doc header.

[obsolete] Move extension compat code

[obsolete] extract serialization logic.

[obsolete] update doc

[state] Update doc on the mutable property of state (and the way it's implemented)

[state] add mutable property to state object.

[states] add a todo related to MQ

[states] fix a bug with rebase --detach There is unexpected (for me) content in state.

[states] add mq support

[states] add rebase support.

[states] move IO logic outside the repository subclass This is meant to lighted this part a bit

[states] add a small paragraph about controlling permision to move the boundary

small refactoring and big doc update. Sorry for the big commit crecord one so much diff seems to confuse my powerbook to death :-/

move part of the readme about states in states itself.

[obsolete] Fix pushkey

Use dedicated mechanism to report pushkey success

[obsolete] Update pushkey code

Update pushkey code to be able to push ready heads too.