Add content to Working with Strings
Update Preparation and add Markdown version
Prepare for refactor of installation process

- Add Makefile (untested)
- Add installation instructions in INSTALL.md. This repalces info formerly in
  .ipynb files.
- Update README.md to reflect the above
- Update Index and "How to use this course"; further work needed.
Remove Notebooks; rename .md to .markdown
Try to get Makefile to work
Refactor content

- Add installation (shell) script
- Fix bug in md2nb.sh
- Shuffle introductory text between files
Remove "Preparation and setup"

- This info now contained in INSTALL.md
Flesh out content in "How to use"
Rename text/variables section and update content

- Rename: Working with text -> Text and variables
- Add a fair bit of content ot this section, incl images
- Replace .svg with .jpg (more stable export from OmniGraffle)
- Minor changes to How to use this course
- Remove erroneously added test.sh
Trash the Makefile

It never worked; GNU make has too many issues with spaces in filenames. Since
this is a simplictic case, it has been replaced with a shell script
(scripts/install.sh)
Fiddle the scripts

- Make the two conversion scripts more verbose.
- Add a pre-commit.sh to convert all .ipynb to .markdown.  This should really
  be a Git commit hook.
Add content to "Working with strings"
Rename Getting Started and flesh out content

- Rename: "How to use this course" -> "Getting started"
- Add two sections to Getting Started:
  - About Python
  - Getting Help
Add "Working with other data"

- This contains
  - ints and floats
  - mixed data
  - booleans