If we include undefined filter values in the encoding/decoding,
then we store 'undefined' as the value in the cookie. When this
gets parsed out, it's treated as an actual value. This will likely
not match anything resulting in the initial filtering to filter out
all results.
Core:
- Added `duplicateSpan` option (default is `true`).
- Renamed `$.tablesorter.formatSortingOrder` to `$.tablesorter.getOrder`.
- Include `table` in console.error if an issue is encountered during
initialization.
- Clean up warning when no parser is found for given data.
- Fix `config.sortVars` js error for non-existent header cells.
- Added unit tests.
- Added "example-colspan.html" demo.
Filter:
- Filters that span multiple columns now have the correct data-column set.
- Consolidated code that parsed data-column ranges into `findRange` function.
- Added unit tests
