Documenting the breaking changes

[Tamas Szekeres]

Folks,

I think it takes a fair amount of work to document the backward
incompatible changes between the 4.10 and the upcoming 5.0 release so
it worth starting this effort in time. Recall that we have a
MIGRATION_GUIDE.TXT in the project tree to enumerate these changes in
a convenient way.

May I suppose that we would want to continue this documentation or we
should open up a brand new one?

Best regards,

Tamas