First draft of the first Intermediate Python lecture

Provides an introduction to Python for scientists with some former
programming background.
Use automatically generated data for Intermediate Python lectures

Instead of making data files up by hand, use a simple model with
error to generate the data.

Includes the code to generate the data (which will be expanded on
later) to allow easily modifying the data if desirable.
Remove material on looping over indexes

This material can be covered in response to questions.
Use single backtick quotes throughout Intermediate Python lectures
Minor editorial cleanup to the first Intermediate Python lecture
Say that .iloc means integer location when introducing Pandas
Split demonstration of DataFrame methods into separate code blocks

This demonstrates the methods one at time making it easier to
follow and also makes the output clearer.
Intermediate Python lectures are for those who have programmed before.

Mention this up front.
Describe difference between Python printing and Notebook displaying.
Execute code block after error message in first Int. Python lecture
Improve display of final figure in first Int Python lecture
Fix typo in image source
Fix typo of Markdown syntax
Fix typos in first Intermediate Python lecture
Adding contributing guidelines.

Includes license, workflow, and file formats sections.
Updating contributions description
Fix typos
Merge pull request #225 from khinsen/fix_typo

Fix typos
Merge branch 'contributing' into master

Cherry-pick CONTRIBUTING.md from
https://github.com/swcarpentry/boot-camps.git

* contributing:
  Updating contributions description
  Adding contributing guidelines.
Move existing guidelines README -> CONTRIBUTING