[rfc] streamline module structure

[Nytelife26]

this is a follow up of #1362, and intends to address issues previously raised in #1155.

Out of scope considerations: cursing, security, links. Each has merits, but they feel out of place in the context of the goal of proselint.

Current plan:

• all checks with one file will be flattened by putting the check file itself into the root directory and renaming it to the category name, both for startup performance ([rfc] startup overhead reduction #1374) and tidiness reasons.
• airlinese, bureaucratese, chatspeak, commercialese, corporate_speak, jargon will all be merged into a new category titled industrial_language (this name is open for discussion)
• security, links, and cursing (except for cursing.nword, see below) will be removed
• sexism, lgbtq, and cursing.nword will be merged into a new category (the name is currently undecided, but may become social_awareness)
• punctuation.spacing will be recategorised under typography, because spacing is a purely typographic matter
• typography.exclamation and hyperbole will be recategorised under punctuation, merging into punctuation.hyperbole for consistency

Condensing considerations:

• mondegreens and malapropisms are commonly grouped together in analysis

A check naming standard will be formed, and referenced in contributing guidelines.