Update documentation - exclude option and dumping relations

1) Try to use a more standard way to display the default value to `exclude` so that it is clear it can be overridden
(I needed to disable the `id` exclusion, and had to read the code before I could understand that this was the case
the current text implies that the `exclude` option applies on top of the 3 default exclusions.. to me)

2) The console API lets you dump arbitrary relations and not just entire tables, add an example to show that
Merge pull request #68 from ktaragorn/patch-1

Update documentation - exclude option's default and dumping relations