Support a user-defined list of pre-formatted indentifiers

In #288, the topic of using a user-defined list of pre-formatted identifiers came up.

At this stage, I am unsure that it is the responsibility of this formatter to modify the casing of identifiers.

Delphi is inherently a case-insensitive language. So the issue of using the right or canonical casing for identifiers is a much bigger job, better suited for a more purpose-built tool. For example, see [sonar-delphi](https://github.com/integrated-application-development/sonar-delphi)'s [MixedNamesCheck](https://github.com/integrated-application-development/sonar-delphi/blob/master/delphi-checks/src/main/java/au/com/integradev/delphi/checks/MixedNamesCheck.java).