^Q would quit even from filter mode

1. Open directories in filter mode
2. Fix arrow keys not working after filter selection (due to invalid cur entry)
3. Support `Insert` key to clear filter prompt
4. Update documentation

1. Strip end spaces and slashes
2. Do NOT change dir if in the same dir
3. Don't go back beyond startup dir with '-'
4. Reset oldpath on cd (other than cd . and ..)
5. Reset filter
6. Update features in README

This change remaps the & key. However, / is more relevant for filter and & makes more sense wrt. address.

It was troubling me. Mimicking 'gg' would have been hacky and would need
additional processing... 'g' was free. Who cares even if you press twice? ;)

We closely follow the output for stat(1).

Add keybind 'Ctrl-k' to copy the absolute path of the file under the cursor if environment variable NOICE_COPIER is set.

1. The detailed view shows file type and size using keybind 'd'. Disabled by default.
2. Option 's' sorts dir entries by descending order of size.

Once set, the default filter is updated.  This means that
toggle dot will also work as expected when noice is executed
as root.

Based on discussion with Ypnose.

Diff by Ypnose

The magic.mgc file gets created in the local directory, opening
the global file throws unwanted messages. So we are using the o/p
of the file command to determine if the file is a plain text file.

Use mpv, fmedia, zathura.
Invoke libmagic to identify text files and open with vim.
Use xdg-open for unhandled mimes.

Original patch written by Richard Hyde and taken from
https://github.com/RichardHyde/noice

Patch written by Richard Hyde and taken from
https://github.com/RichardHyde/noice

Nobody uses it and adds additional complexity.

Specifying commands by name in config.h means that
every time one switches ones editor (for example),
one has to modify every config.h file referencing that editor
and then recompile every corresponding program.

This change adds a string `env` for specifying an environment
variable to `struct key` and uses it to optionally specify the
command to run on SEL_{RUN,RUNARG}.
The `run` string is used as a fallback when the environment variable
has not been specified or is not set.
It also updates `config.def.h` to demonstrate this new capability.

Disable timeout when in filter or type mode.

This reverts commit 1e18b85e56.

Revert until remaining issues are fixed.  The filter search expires
after 1 second of inactivity without the revert.