Feature: Format command rewriting the file completely according to some rules

[yoheimuta]

ref. #139 (comment)

vs. -fix option:

• -fix option is so conservative that it doesn't force an opinionated format by following the explicitly specified rules with granular settings. While it's useful, sometimes it's too complicated to implement editing only a small fraction of the file content.
• format command is supposed to be an opinionated feature so that it can fully rewrite the file content according to the choice of some predefined styles. It would be expected to complement the -fix option.

For example, I presume it results in easier support for the file structure guidelines.

[yoheimuta]

Practically speaking, I've done this issue with #111.
For now, I will close this issue.