Provides workaround for nested scripts

[myxoh]

This is a solution to: #127

Regarding the solution:
I found that there was no easy way to sort this at the node level, as the problem is specifically that sibling nodes could, together after destroying a middle node become problematic.
I chose to restart a clean on fragments and documents if their representation raw_text was deemed to be problematic.

Regarding defaults:
Due to some existing expectations on the specs, the proposed solution is not 100% retrocompatible, hence I introduced the new 'safer' method recursive_scrub_fragment (and document).

Regarding testing
I did integration testing to make sure that: we are modifying the behaviour as slightly as possible.
We solve the nested script validation issue.

[flavorjones]

I'm looking at this now. Thanks for submitting.

[flavorjones]

Please see discussion at #127 which I'd like to understand before commenting on this approach.

[flavorjones]

Note that I've addressed example 1 in #127 with #132 which I feel is more obvious and more targetted.

I'll leave this open while we continue the conversation about examples 2 and 3 in #127.