[Feature] Support dark-mode on Windows.

[seagle0128]

Use powershell to check if dark-mode is enabled on Windows.

Close #16

[LionyxML]

Woooow, thanks @seagle0128!!!

I'll take a look at it, probably near the weekend :)

Meanwhile, a couple of questions:

• Is PowerShell installed by default nowadays? Should we add it as a a requirement?
• Does it work with base emacs windows binaries (like those found in http://ftp.gnu.org/gnu/emacs/windows/), or does it require a special build?

Thanks!

[seagle0128]

• Is PowerShell installed by default nowadays? Should we add it as a a requirement?

Windows PowerShell comes installed by default in every Windows, starting with Windows 7 SP1 and Windows Server 2008 R2 SP1. See https://learn.microsoft.com/en-us/powershell/scripting/windows-powershell/install/installing-windows-powershell?view=powershell-7.2. If powershell doesn't exist, auto-dark--is-dark-mode-powershell always returns nil.

• Does it work with base emacs windows binaries (like those found in http://ftp.gnu.org/gnu/emacs/windows/), or does it require a special build?

It works with any emacs build on Windows.