Allow Use of Multiple Ranges When Setting Style

[oleibman]

Fix #411, which went stale in 2018 and is now reopened. You can get a style for a set of cells which uses multiple ranges, e.g. A1:B2,C5:H10, but we throw an exception if you try to change the style. I don't know how useful that is, but it's been requested and it's pretty easy to implement with recursion.

The comma in the ranges represents the union operator. getStyle is very permissive - it will allow almost anything to be specified. However, attempts to use a space as the intersection operator, or, indeed, many other nonsense strings, will still be permitted for getStyle but will continue to throw an Exception if an attempt is made to alter the style.

This is:

• a bugfix
• a new feature
• refactoring
• additional unit tests

Checklist:

• Changes are covered by unit tests
  • Changes are covered by existing unit tests
  • New unit tests have been added
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change and a link to the pull request if applicable
• Documentation is updated as necessary