Strings improvement: trim ZWSP char

[CrazyMuffin]

• new feature
• BC break? yes - if someone relies on having ZWSP non-trimmed while using default parameter.
• doc PR: Not needed, function is covered and does not mention the default characters

Sneaky Zero-Width Space char \u{200B} is currently untrimmed by trim function, while I'd expect it to do so.

Workaround:

1. Fork or extend the class and overwrite default param
2. Manually set updated charlist as second argument to every trim() call

[dg]

Thanks