Marcxml-parser

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- Fixed ability to query tags codes using indexing operator.

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- Updated set of possible `i` characters.

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- Fixed bug in the publication type parser.

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- Implemented ``.get()`` method.

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- Fixed typos in documentation.
- Added ``record_itrator()``.
- Added support for file-like objects.
- ISBN is now discriminated to valid and invalid. Added new method ``.get_invalid_ISBNs()``, ``.get_ISBNs()`` now returns just valid ISBNs.
- Fixed bugs in ``.get_binding()``.
- Added field ``URLu`` to output from ``.get_internal_urls()``.
- Added one more test.
- Fixed few typos in documentation.
- Added support for ISSN querying.
- Fixed bug in ``run_test.sh``.
- Fixed parsing of the place to reflect changes in RDA.
- Added more RDA fixes.
- Fixed bug in parsing of the dates.

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- Fixed small bugs in code and documentation.
- Added more tests.