Wikitextparser

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- BREAKING CHANGE:
Remove ``replace_bolds``/``replace_italics`` params from ``remove_markup``/``plain_text`` methods.
Users can use the new ``replace_bolds_and_italics`` parameter. Removing only bolds or only italics is no longer possible.
- Add ``get_bolds_and_italics`` as a new method.
- Fixed bugs and rewrote the algorithm for finding ``Bold`` and ``Italic`` objects. (51)

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- Trying to mutate an overwritten/detached object will now raise ``DeadIndexError`` (a subclass of ``TypeError``). Hopefully this will prevent some subtle late-appearing bugs.

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- Fix a bug in ``plaintext`` method.

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- Fix a bug in detection of external links in parsable tag extensions. (50)

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- Fix a bug in handling of half-marked bold/italic, e.g. ``'''bold\n``.

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- Fix a bug handling of half-marked bold/italic items e.g. ``'''bold text\n``.