ImageMagick version 7 provides command 'magick' (as well as legacy 'convert'), is readily available on Windows but is not, currently, readily available on Ubuntu.
On Windows, the name of ImageMagick's `convert` utility clashes with Microsoft's `C:\Windows\System32\convert.exe` utility. Using `magick`, if available, avoids the conflict.
For clarity and to be command name-agnostic, the raster option name is changed from 'convert' (the command) to 'imagemagick' (the name of the software).
For consistency with the version 7 command name, references in the code to 'convert' are changed to 'magick', throughout.
* First docs.
* Docs requirements.
* Add auto-generated gallery and fix two bugs in the driver.
* Gallery: link directly to github.
* Tag examples as Haskell code.
* Update starting guide and redirect gallery links to master branch.
* Include link to readthedocs.
Former-commit-id: 90e846e5001deadd6c921f611c69b3a4210db30d