Clarify how to use regular expressions

[mpkorstanje]

https://stackoverflow.com/questions/54081489/cucumber-3-how-to-define-a-regular-expression

Leads me to believe the docs do not cover this well.

1. Create page like cucumber-epressions for regex.
2. Mention in step def and cucumber expression pages.
3. Remove wikipedia links.

[mlvandijk]

This might be helpful: https://agileforall.com/just-enough-regular-expressions-for-cucumber/

[mlvandijk]

Note: With the introduction of cucumber expressions all regular expressions should start with ^ and end with $.

[mlvandijk]

See also cucumber/cucumber-jvm#1595

[mlvandijk]

See also #497