Adopt PHP Internals abbreviation capitalization rules

[Crell]

Replaces #83

PHP Internals has adopted guidelines for when and how to handle capitalization of abbreviations in class/method names. We should follow suit and just steal their language directly, and/or just link to it. Whether we copy or link is really the only question. (I'm open to either at the moment.)

cf: https://github.com/php/php-src/blob/master/CODING_STANDARDS.md#user-functionsmethods-naming-conventions