New "dataFilterValue" and "dataNoFilter" options to allow filtering using "data-" HTML5 attributes

[e-picas]

This one is a totally new feature (!) and has to be tested (I use it and it seems to work but I may have miss some cases ...).

The idea is to allow developers to choose what will be filtered defining a data-XXX=YYY attribute in a td element, which will be used to match the filtering string instead of the content of the td. Another data-ZZZ attribute can be defined to NOT filter a cell at all.
The rule is quite simple:

• if a td have the attribute defined, even with an empty value, this value is used instead of the td content
• if another td does not have the attribute, its content is used (like the original behavior).

Original commit message:

• adding the « dataFilterValue » and « dataNoFilter » options in js filtering
• new « filtertable-sample-data-filtering.html » example
• new options in the README for data options how-to

Notes:

• I added the word "modified" to the version number in JS files (for info)
• I made the minified version with an ugly online tool ...