NOBLINK, NOTSHIELD, correct SS pins for 1284P

- Ability to disable bootloader blink
- Ability to disable SD SS pin state change
- Standard Ethernet Shield(and Ethernet library) W5100 and SD SS pins
for all ATmega1284P variants
- Remove all ATmega1284P variants except for avr_developers. This is the
only variant with a license so until I can get licenses for the others
Mighty 1284P will need to be installed to add support for those boards.
- Update documentation

NOTE: For some reason using 57600 baud rate for ATmega1284P 8MHz causes
serial upload not to work. They will only work with 115200 baud rate.
this forced me to make separate 8MHz boards entries in more-boards.txt
instead of being able to add a 8MHz option to the Clock custom menu and
using the 16MHz bootloader file at 57600.

Add Boards Manager install instructions

Merge pull request #18 from jkramarz/patch-3

Update README.md