Optimise --filter option pattern

[gerardroche]

The current --filter option just joins a list inside a or regex pattern:

def build_filter_option_pattern(list):
    return '::(' + '|'.join(sorted(list)) + ')( with data set .+)?$'

The pattern could be optimised to avoid really long patterns.

Also, maybe we should put a limit on the size?

[myself379]

Cool ideas!