Allow php-cs-fixer to Handle Implicit Backslashes

[oleibman]

Its defaults are to unescape within single quotes, and escape within double quotes and here-docs. Right now, it leaves everything as-is, which means our code is inconsistent and need not be. Further, although dealing with complex regular expressions will never be easy, I find it much easier to figure out what's going on when superfluous back-slashes are removed.

These changes were all made automatically using the "fix" script, so should be reliable. They, of course, pass all unit tests.

This is:

• a bugfix
• a new feature
• refactoring
• additional unit tests
• more consistent code base

Checklist:

• Changes are covered by unit tests
  • Changes are covered by existing unit tests
  • New unit tests have been added
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change and a link to the pull request if applicable
• Documentation is updated as necessary