allow search term parameters (include and exclude) in qiime taxa filter to be specified multiple times

[gregcaporaso]

Improvement Description
Allow search term parameters (include and exclude) in qiime taxa filter to be specified multiple times. This would more closely match how we handle "multi-inputs" in other parts of the ecosystem, for example the multi-file options to qiime metadata tabulate.

Current Behavior
Multiple search terms are provided as comma-separated text, e.g, --p-exclude mitochondria,chloroplast.

Proposed Behavior
Multiple search terms would be provided by specifying the parameter multiple times, e.g, --p-exclude mitochondria --p-exclude chloroplast

Comments

1. It probably makes sense to continue supporting comma-separated text for a couple of releases, raising a VisibleDeprecationWarning if a user provides comma-separated text.