Added support for custom filtering functions.

[dadittoz]

I didn't add any tests for configuration. Existing tests pass correctly. Pull it if you like.

[holli]

I'll leave it here for the time being.

This would need better tests and some info in the Readme.md before pulling.

For someone who is thinking of using the plugin. This patch allows to add custom filtering functions in initializers. Quite handy for sanitizing html, some specific numbers, etc. I guess example would be something like:

AutoStripAttributes::Config.set_filter :remove_html do |value|
  Sanitize.clean(value, HTML::RELAXED)
end

[holli]

@dadittoz if you have better examples etc. You could include those in the Readme.md after current examples and make some tests for those custom validators.

Otherwise I'll pull when I need that feature for myself for the first time :)

[dadittoz]

Looks like that's it. Let me know if you anything else should be added.

[holli]

Cool, thanks for the patch.

I did some minor things:

:nullify is now with
(value.respond_to?(:'blank?') and value.respond_to?(:'empty?') and value.blank?) ? nil : value

so that tests go right with both ruby 1.9 and 1.8.7. Also bit more tests included.

I bumpt version to 2.0 and added info to readme about versions (and reference to this pull request/issue). New version is in rubygems.