Change abbreviation guideline

Currently we have separate rules for abbreviations and acronyms. This proposal brings those together into single rules. The existing rules do not match which what most code does with well-known abbreviations such as: ID (Identifier), Company abbreviations, DB (Database), TM (Trademark), Cert (Certificate), Sig (Signature), etc.

Proposal: Change the following guidelines:

:x: DO NOT use abbreviations or contractions within identifier names.
:x: DO NOT use any acronyms unless they are widely accepted, and even then use them consistently.
:heavy_check_mark: DO capitalize both characters in two-character acronyms, except for the first word of a camelCased identifier.
:heavy_check_mark: DO capitalize only the first character in acronyms with three or more characters, except for the first word of a camelCased identifier.
:x: DO NOT capitalize any of the characters in acronyms at the beginning of a camelCased identifier.

To be:

:x: DO NOT use contractions within identifier names.
:no_entry: AVOID use any acronyms or abbreviations unless they are widely accepted, and even then, use them consistently.
:heavy_check_mark: DO capitalize only the first character in acronyms or abbreviations with two or more characters, except for the first word of a camelCased identifier.
:x: DO NOT capitalize any of the characters in acronyms or abbreviations at the beginning of a camelCased identifier.