Minor rework of SK6812 EC15

An annoying one, because NeoPixels are pain. But a good "maker" part to keep up to date.

• Fab arrow to outline so it's not so "blobby" when printed
• Fab text size to 0.5mm minimum - it still fits three characters (D + 2 digits)
• Same for silk size
• Silk moved 0.2mm from copper
• Pads to rounded
• Updated description, especially to include "orientation mark at VDDGND", following LED_PLCC-2_3.4x3.0mm_AK

Questions:

• I didn't rotate it as putting the "feature pin" pin 4 at top left collides the fab ref des with the orientation arrow
• DS is a dead link. Options:
  • Archived: https://web.archive.org/web/20210226212107/http://www.newstar-ledstrip.com/product/20181119172602110.pdf
  • Not a PDF: http://ledstrip-china.com/productshow.asp?id=322
  • Plus a bunch of scribd links!

These are for SK6805-EC15, which seems to have a different pin marking:

• JLC, no PDF link: https://jlcpcb.com/partdetail/OPSCOOptoelectronics-SK6805EC15/C2890035 - doesn't show pin 4 marking
• Shenzhen Normand: http://www.normandled.com/upload/202003/SK6805-EC15%20LED%20Datasheet.pdf (also no pin 4)