Clarify Qarcoal case sensitivity

[gibsramen]

Note that Qurro's text searching is case insensitive while currently Qarcoal is case sensitive (uses pd.Series.str.contains).

Should deal with this in Qarcoal - probably easiest to just add an optional flag to specify case sensitivity (and make sure its clearly defined as such to the user). Default should probably be case insensitive to match Qurro.