Consistent naming of writers

[noelwelsh]

There are several types that convert a Picture into something else:

• Writer
• Base64
• BufferedImageConverter

There will probably be a lot more in the future. Let's name this concept and have a consistent naming scheme for the types that implement it.

I propose calling this a writer. Methods on different writers will be different (e.g. a FileWriter will take a file name, where as a Base64Writer will not.) but it is possible to implement a marker trait, as is done for Algebra and Format.

• [ ] Implement Writer marker trait
• [ ] Update existing Writer, Base64 etc to extend marker trait
• [ ] Rename to FileWriter, Base64Writer, etc. for consistent naming
• [ ] Update syntax accordingly
• [ ] Document

[jCabala]

Should the documentation be written in the effect specific README.md file?

[noelwelsh]

Documentation lives here: https://github.com/creativescala/doodle/blob/main/docs/src/pages/README.md