Add screen blanking using a full size X window

[alexyuriev]

• a black window stretches over entire workspace including multiple displays
• a window manager decorations are turned off on this window ( Tested in OpenBox )
• cursor is turned off

[dannydulai]

I'm happy to pull this in, but there needs to be some cleanup stuff here:

1. make your new changes a new "mode" that can be triggered by argv or by env var (your choice).
2. old code path should exist, unchanged, when your new blanking mode is not activated
3. please conform to the spacing/tabbing from the previous file so there are not a bunch of whitespace related diffs added.

[alexyuriev]

1. ok that's easy.
2. same
3. what is your standard? Because my editor could not figure it out.

[dannydulai]

4 character indent, 8 character tabstop

[alexyuriev]

One more question. What's your license on XL since it is not specified?

[dannydulai]

bsd 3 clause -- added file.

[lukelex]

RIP