remove i2c driver function calls and directly read/write I2C->DR
reformat I2C driver and align comments. add timeout checking and move hardware reinit common code into separate function.
moved nvic priority group init into drv_system, where it belongs
Remove FY90Q support. Dead hardware, not even available anymore, and doesn't offer anything over already cheap acroafro.
fixed ADC initialization with skipped channels  - spotted by Lux.
Also increased ADC sample time to 239.5 cycles (~10uS at 24MHz ADC clock).
current sensor support added

also optimized the vbat code a bit
Merge pull request #113 from luggi/Powermeter

Current sensor support added, with defaults for Allegro ACS758 current sensor.
Merge remote-tracking branch 'multiwii/master'