Per mapper configuration support

[stefankoppier]

Is your feature request related to a problem? Please describe.
Currently, configuration options can only be applied globally. Sometimes, you want to apply configuration only locally, e.g. per mapper.

The global options should be the default, per mapper options should override these global options for the specific mapper.

Describe the solution you'd like
Sevaral solutions are available:

• An options { ... } block in the mapping function.
• A seperate overridable options function from the abstract base class.