Micro: Show invisibles (whitespaces, tabs, newlines...)

[KhodeN]

Would you add feature/option to show whitespaces?

Spaces as small dots, tabs as arrows

[mikamiel]

And LF, CR, CR+LF as paragraph mark ¶

[zyedidia]

This would would be an extension of the indentchar setting. I think it's probably best to implement the way Vim does with listchars with a list of all the different special characters.

[moqmar]

And please display undisplayable Unicode characters in a hexadecimal format - it happens so often that micro puts some escape sequences into files for whatever reason (probably related to #779), but without that feature it's impossible to debug that without starting vim or basically any other editor.