Support writeback

[MisanthropicBit]

This is a breaking change due to item 1 and 6 and probably 5 as well.

1. Less invasive default preview mappings.
2. Clean up float and page modules.
3. Remove unused string utilities.
4. Fix deprecations.
5. Better support for newlines.
6. Rename config.float.options to config.float.win_options and config.float.mappings.jsonpptoconfig.float.mappings.json` in config.
7. Add config.float.zindex option to config.