v1.1.1 - Improved documentation - pinout diagrams, bugfixes

This release introduces improved documentation including new pinout diagrams by @MCUdude, who also maintains several cores for the larger ATmega microcontrollers.
Additional changes and fixes:

• Fixed issues with avrisp and avrispmkii programmers
• Added missing digitalPinToInterrupt() macro
• New bootloader for ATtiny828 @ 5v to work around voltage dependence of internal oscillator frequency.
• Removed unsupported material from board manager release ("old" optiboot and nomillis core)
• Removed unused "empty bootloaders" - all devices now use the same "empty_all.hex" which contains just a couple of bytes (as avrdude will refuse to write the fuses if you tell it to write an empty file to the flash).