Support MS Windows

[alexluigit]

For now I noticed 3 issues when using Dirvish on MS Windows:

• image / pdf preview doesn't work
• the disk name is displayed incorrectly on mode line.
• dirvish-peek-mode doesn't work properly (the file being previewed should not take up the focus)

I'll see if they can be fixed.

BTW, In the past few months I have been held back by some other things, as a result I don't have much time to maintain this project. I am sorry for this.

[jkbhagatio]

For me, mode line also doesn't display correctly

[sho-87]

fyi #224 seems to be an issue on windows as well