Feature Request: enhance display line number, by adding a filter field to exclude files types (.txt, .md)

[artofit]

 * Xed version (xed --3.2.7)

Issue
Feature request:
Under preferences>Editor
one can toggle on/off the fact of displaying line numbers

This feature applies to all files, either you want it or not.
If it is very convenient for programming,
so files such as .c, .ino, .js, .css, etc
it is not desirable for text related files such .txt, .md

Therefore I, as the list of programming files can be consequent(.sql, .cpp, .java, ...),
I propose the following small change.
See
add a text field under the line for the option to toggle on/off, so that
when toggle ON, displaying line numbers applies to any files, to the exception of listed files in the text field.

Thanks
P.S. I found the red color of files excluded, to be a good choice to show the exclusion.