Add Boards Manager JSON file

[per1234]

Adds Boards Manager install support for ATTinyCore and arduino-tiny-841.

• Boards Manager install URL for testing: https://raw.githubusercontent.com/per1234/ReleaseScripts/add-JSON-file/package_drazzy.com_index.json
• More info links are to:
  • https://github.com/SpenceKonde/ATTinyCore
  • https://github.com/SpenceKonde/arduino-tiny-841
• Install tested with Arduino IDE 1.6.5r5 and 1.6.6 Hourly Build 2015/09/18 06:03
• Note: There is a bug(Entry for newly added URL doesn't appear the first time Boards Manager is opened arduino/Arduino#3795) in the hourly build that requires you to open Boards Manager twice before the entries for a newly added URL will appear.

Happy to make any changes, just let me know.