* non builtins options require declaration using the decl command
* At the moment, only int and string options are supported, however
the goal of this change is to provide a consistent way to support
more complex options, namely lists and booleans
- use set_option to set an option, instead of operator[] (no-const)
- keeps a list of OptionManagerWatcher to notify when an option change
it also notifies when an option changes in his parent and the option
is not overridden.
OptionManager map names to options, and may delegate option resolution
to it's parent if it does not contains the asked for option. That way
Buffers can override global options, and Windows can override Buffer
options.
