votes html scraper should not fail silently by default

following PR #3 - it looks like in case an unknown member is encountered it will fail silently

in knesset-data-python we would like to be as low-level as possible and make as little assumptions as possible about how the data will be used

in this case, silently ignoring an error might cause unexpected problems down the line

I prefer that by default we will raise an exception, and add a skip_exceptions parameter which will instead of raising an exception yield the exception object as part of the data stream - to allow the end-user decide how to handle the exception

this is done in the dataservice scrapers, see for example this unit test -
https://github.com/hasadna/knesset-data-python/blob/master/knesset_data/dataservice/tests/base/test_exceptions.py#L38