substantially restructure all quantized docs to group logically (#27677)
Summary:
Make everything clickable
Organize APIs logically in subsections
Fix many typos
Pull Request resolved: https://github.com/pytorch/pytorch/pull/27677
Differential Revision: D17850650
Pulled By: dzhulgakov
fbshipit-source-id: 060f6ed988d1c4beecba6bc8daf55626961fac98
