[RFC] Clarification on formatting for bangs (!)

It seems to me that 
> Add a single space around operators

would mean using the practice on the bang operator as well; as discussed in [this thread](https://github.com/php-fig/fig-standards/issues/102), there is somewhat of a conflict--so this may not be the way to go. If the PSR could be amended, then this change would make sense.
Reverses statement about bang spacing and corresponding examples
Adds bullet addressing bang placement
Fixes wrong bullet character
Fixes spelling and formatting errors
Adds missing space before return statement
Changes operator spacing language
Incorporates @WouterJ 's suggestion for more realistic usage of bang
Fixes concat operator typo
feature #4457 [RFC] Clarification on formatting for bangs (!) (bryanagee)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #4457).

Discussion
----------

[RFC] Clarification on formatting for bangs (!)

It seems to me that
> Add a single space around operators

would mean using the practice on the bang operator as well; as discussed in [this thread](https://github.com/php-fig/fig-standards/issues/102), there is somewhat of a conflict--so this may not be the way to go. If the PSR could be amended, then this change would make sense.

Commits
-------

ee888c6 Fixes concat operator typo
33e76a5 Incorporates @WouterJ 's suggestion for more realistic usage of bang
837e895 Changes operator spacing language
835d5eb Adds missing space before return statement
3799bc0 Fixes spelling and formatting errors
30d19ab Fixes wrong bullet character
3212b6c Adds bullet addressing bang placement
95a1cc5 Reverses statement about bang spacing and corresponding examples
a68d3e5 [RFC] Clarification on formatting for bangs (!)