Dhtmlparser3

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- Bugfix; SpecialDict.copy() didn't return any value.

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- Bugfix; Don't search empty tags.

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- Bugfix; Always return container element for small doms with only strings inside.

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- Added `.__hash__()` method for Tag.
- `.replace_with()` method now accepts `str` as well as Tag.
- Fixed problems with `.parent` setting for non-pair tags in the parser.
- Added bunch of tests to test newly added stuff.

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- Added `.__contains__()` method for Tag, so you can now test parameters using `in` operator.

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- Rewritten to use different parser, support for HTML entities.
- Structure of the classes completely changed, now Tag & Comment are used instead of HTMLElement.
- Much more cleaner code and more comprehensive method names.
- By default, the tree is now double-linked without any additional cost.
- Implemented very useful magic methods, so indexing operators are supported for access to both parameters and content.
- Documentation completely reworked.
- Set of coverage tests is now much larger.