Merge pull request #30 from hadleyrich/master

Add quirk for ADC_REFSEL_INTVCC_gc
Correct detection of 256A3B family.
Closes #25
ADC vref finally resolved. (Bad release by Atmel, don't use AVR8 Toolchain 3.4.3)
Add VCC/2 reference source.
Include the license used.
Refactor system clock API
Removed sysclk_init(), replaced with kakapo_init()
Remove sysclk_uptime() and related functions.
Moved interrupt enable to kakapo_init().
Clock setup checks dependant config has been done.
This partially resolves #2.
Change examples to use kakapo_init() instead of sysclk_init()
Restore workaround for bad ADC ref names.
Merge pull request #1 from dave2/master

Update repo from master.
Fix typo. It is ADC_REFSEL_VCC_gc not ADC_REFSEL_IVCC_gc
Merge pull request #31 from thewizzy/master

Typo in the adc.c definition
Move detection of number of event channels to global.h
RTC driver.
RTC driver example.
Fix error checking logic and define typo in clock_rtc
Add rtc to Makefile