Documentation conversion into Mkdocs

[daexs]

Converted the plotly.py documentation build into Mkdocs

• Create a Mkdocs build for the plotly.py docs and reference pages, including styling.
• Modifies the code generator to create output that is compatible with Markdown rendering. For example, \\\\[i\\\\]\\\\[{i}\\\\] ensures that Mkdocs will correctly render this portion of the docstring into [i][i].
• Modifies the examples for any code block errors, jupyter special commands, and formatting issues. For example, lists do not render correctly unless a new line was added.
• Modifies link references within example and reference pages for readability and converted url links into internal markdown links for Mkdocs to handle.
• Home/Landing page is plotly/plotly.py/README.md and index pages are placed in each individual category of examples under Overview.