chore: reduce boilerplate code for ngx_module_t declarations

[xeioex]

This partially addresses #107.

[bavshin-f5]

Still not convinced the commands initialization change is right. It assumes constness where we shouldn't, and could be less readable with a larger set of commands.

[bavshin-f5]

ngx_module_t::default and CONF_OFFSET changes look good. I'm ready to cherry-pick these to master if you split the CONF_OFFSET patch and reorder both before the prelude one,

I have reservations about the prelude patch though. Maybe we need more high-level wrappers before introducing this.

Note: refactor!: prefix to the commit summaries seems more fitting. See https://www.conventionalcommits.org/en/v1.0.0/#summary and https://github.com/angular/angular/blob/22b96b9/CONTRIBUTING.md#-commit-message-guidelines

[bavshin-f5]

Pushed e834149 and 4ee19c0 to master with minor adjustments.