document mbr

closes #202

Signed-off-by: Maximilian Güntner <maximilian.guentner@gmail.com>
Merge pull request #221 from mguentner/mbr_docu

document mbr
added e6-style definitions for Timer/Counter3 on 1284p
added e6-style definitions for Timer/Counter3 on at90can32/64/128
fixed bit names for COM3An
fixed use of register names TCCR1A/B and MCUCSR, added e6-style definitions for Timer/Counter3 on atmega162
fix bitmask for TC1/TC3_PRESCALER_64 for at90can32/64/128
fixed bitmasks for TCn_PRESCALER_xy
fixed bitmasks for TCn_PRESCALER_xy
fixed bitmasks for TCn_PRESCALER_xy
fixed use of register names TCCR1A/B, fixed TCn_PRESCALER_xy bitmasks, added e6-style definitions for Timer/Counter3 on atmega64
fixed TCn_PRESCALER_xy bitmasks, added e6-style definitions for Timer/Counter3 on atmega128
fixed Timer/Counter3 TIMSK and TIFR bits
whitespace cleanup
removed redundant define MCU_HAS_TC3
Merge pull request #226 from michaelb42/e6_add_Timer_Counter3_support

Add Timer/Counter3 support, fix issues #223 and #225 for several controllers
converted timer SD_PING_READ m4-inline-code into function, added proper config dependency
converted timer with IPV6 router solicitation m4-inline-code into function, fixed broken interval handling, added proper config dependency
added proper m4 config dependency instead of borked preprocessor inline code
converted timer for tcp and udp connection handling m4-inline-code into functions, added proper config dependencies