Update license file to match Github expectations

- Use " and ' instead of curly quotes
    - Current quotes come through as question marks on some systems
    - Proper quotes (`U+2019`, `U+201B`, `U+201C`, `U+201D`) come through strangely on Github
- Consistent whitespace throughout
    - Double spaces in some places changed to single space
    - Tabs replaced with spaces
    - 4 spaces used for indentation (instead of 5)
    - Removed indentation for first level list items (bottom half)
- Renamed `license.txt` to `license.md` to take advantage of automatic formatting
- Changed `a.` to `1.` under 2.7 to get it to be parsed as markdown
- Wrapped to 80th column (standard)

Feel free to cherry pick these changes as needed.