Parse categories correctly (they are often comma-separated).

[kfogel]

Category columns often include multiple categories, separated by some delimiter (usually a comma).

Right now we're treating the entire content of a category cell as one big category. Instead, we should parse it and apply all of the resultant categories. This may involve adding a new cat_delim config option, defaulting to comma.

[kfogel]

Based on OpenTechStrategies/torque-sites#19, this may be a non-issue. Leaving it open for now, but it may get closed with no further action once we confirm.

It could still be a nice feature, but let's wait until some real-world user is actually asking for it.