Moves the lint back from pedantic to style group.
The lint default now only warns on names that are completely capitalized, like "WORD"
and only if the name is longer than 2 chars (so that names where each of the letter represents a word are still distinguishable).
For example: FP (false positive) would still be "valid" and not warned about (but EOF would warn).
A "upper_case_acronyms_aggressive: true/false" config option was added that restores the original lint behaviour to warn
on any kind of camel case name that had more than one capital letter following another capital letter.
The lint does point out inconsistency with the Rust naming convention,
but the fact that rustc does not warn about the inconsistency by default
means that clippy probably should not warn by default either.
changelog: move upper_case_acronyms lint from style to pedantic group.
