Multiple minor fixes to notebooks under tutorials directory

[frreiss]

This PR groups together a number of minor fixes to the notebooks and Python files under the tutorials directory. Summary of changes:

• Fixed path issue that caused CoNLL_2.ipynb not to run
• Added one more cell to CoNLL_2.ipynb to generate the example DataFrame used in the PyData Montreal talk.
• Fixed a minor typo in a comment in Market_Intelligence_Part1.ipynb
• Edited the Markdown text of Market_Intelligence_Part2.ipynb based on edits from the Medium blog version
• Added the code-only notebooks, drawn directly from Market_Intelligence_Part1.ipynb, that were used in the PyData Montreal demo.
• Removed unnecessary cells from one of the Github gist notebooks for Market_Intelligence_Part2.ipynb
• Removed unused code from market_intelligence.py and synced some functions with their Github gist versions.

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[frreiss]

@BryanCutler do you think you might have a chance to review these changes? I have some other changes queued up behind them.