Feat/add option to exclude fields

[paulheijman]

Sometimes it's more practical to exclude specific fields instead of listing all the fields you want to export.
The -e argument lets you define a comma separated list of fields to exclude from the documents.

E.g.:
-s "foo, bar, baz" -e "bar, quux"
will export only the foo and baz fields because bar is excluded. quux is ignored in this case because it is not in the select list.

If -s is not given it will use all fields minus the ones in the exclude list.

[juarezr]

@paulheijman,

Would you mind running the following command to appease the CI verification:

cargo fmt

:-)

[paulheijman]

Did the cargo fmt ;-)