Striplog

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- We are no longer supporting versions of Python before 3.6 (because I like f-strings).
- You can now pass format string labels to ``striplog.plot()``, e.g. ``'{colour} {lithology}'``. These are passed to the Component summary method.
- The Striplog constructor now creates Components if it is given miscellaneous data. If there are not components (e.g. "comp" fields in the CSV), then the description and either the provided Lexicon or the default one will be passed to the Interval constructor.
- Reorganized and moved ``the documentation <https://code.agilescientific.com/striplog>``_ to make it a bit easier to follow.
- You can plot Striplog's logo with ``striplog.logo.plot()``.

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- Added ``Striplog.from_dict()`` to create a striplog from a dictionary with items like ``name: depth``.
- When reading a Petrel 'tops' file, you can pass a single function to apply to every quantity, not just a mapping of field names to functions. (You might do this to replace all ``-999.25`` with ``np.nan``, for example.) There's no way to do both at present, but if there's a need, please file an issue.
- Updated the default lexicon with some 'modifiers' like 'silty', 'sandy', etc.
- ``Lexicon._parse_description()`` is now a private static method (it was previously mangled which was a mistake). It can be called without instantiating a class to parse a piece of text. See the notebook, ``Parsing_a_description.ipynb``.
- Fixed a bug causing the default Lexicon to be a shallow copy, which was annoying.

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- Breaking change: ``Striplog.extract()`` now returns a copy of the striplog instead of changing the striplog in place.
- Added option to send actual data to ``Striplog.to_log()`` instead of index from lookup table.
- Added a tutorial, ``Blocking_curves_with_striplog.ipynb``.

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- Multi-step Markov chains now work properly, respecting 'self-transitions'.
- Added ``include_self`` property to the repr of a Markov chain object.
- Added ``match_only`` argument to ``Legend.random() to allow you to keep only certain properties in the components.
- ``Component.from_text()`` will now use ``Lexicon.default()`` if you don't pass one in.

We started adding an experimental new feature; feedback welcome! Added ``Striplog.from_macrostrat()`` which takes a lat/lon location and returns a striplog in geological time or in depth below the surface at that location.

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- Fixed sphinx documentation.
- Documentation now includes all tutorial notebooks.

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- Added ``label`` kwarg to ``striplog.plot()``. Give it the name of a field in the ``primary`` component and it will be added to the plot as text. Experimental feature; might break with some sizes of striplog. Feedback welcome.
- Fixed a bug in ``Striplog.hist()`` which produced the wrong colours and labels for the bars.