[Feature Requests] add some handy functions

[zhlinh]

The app is awesome, but want to add some handy actions: [Feature Requests]

1. "core.path.file": copy filename only, currently there are core.path and core.path.folder
2. "core.select.group.ext": select the same ext file with the file on current cursor
3. "core.select.group.filename": select the same filename with the file on current cursor which in flat mode can be used to remove the duplicated files
4. "core.ordering.filename": sort by filename
5. "core.ordering.ext": sort by ext
6. "core.ordering.size": sort by size
7. "core.ordering.modifiedtime": sort by modifiedtime
8. favorites can be set by user with any alphabet, not just number 1~5
9. "core.flatten.toggle": The toggle will be useful when set flatten to mapping
10. "core.preview.inactive": preview in the inactive window

[BUG? maybe]

1. "\": this mapping can not work, when set mapping like "\" "core.select.invert"
2. ";": this mapping can not work, when set mapping like ";" "core.select.none", this will be set if the "'" key is set Thanks for reading.

[zhlinh]

[marvelph]

"core.path.file": copy filename only, currently have core.path and core.path.folder

I believe there is a ‘core.clipboard.copy'.