Add option for formfeed characters

[ian-kelling]

Currently, they are deleted by default as whitespace at the end of the line.
I think they should not be removed by default, and maybe an option
added to remove them. They are part of many gnu programs that
have very very widespread use:
https://www.gnu.org/prep/standards/standards.html#index-formfeed
These characters are also known as ctrl-L ^L, ascii character #12

[ian-kelling]

Note, these characters do not show up "as whitespace" in emacs or vim, they show
as ^L. So, for code, I don't even consider them to be whitespace.
The reason they are considered whitespace by regex is because they are whitespace for purposes of printing physical copies. But in that circumstance, they are always
significant whitespace, you would never want to delete them.

[ian-kelling]

*would not want a general rule to always delete them.

[dlenski]

Interesting 🤔

Perhaps we need a way to customize which characters get considered as whitespace/non-whitespace (rather than just relying on \s and \S) in the main regex…?

Want to code something up and submit a PR?