WIP - Implement I2C through DMA #94
Updated DMA config code
Updated TwoWire_DMAConfig() method
Updated Master Mode
Uncomment TwoWire's Slave Mode code
Removed Master EV handling code(We use EV handler only for Slave mode)
Enable I2C Event Interrupts only for Slave mode operation
Updated Slave Mode code
Slave mode not working as expected (WIP)
Completed and Tested I2C Master/Slave Mode using DMA/Interrupts
Added Wire.speed() method and master/slave transmitter mode bug fixes
Renamed Wire.speed() to Wire.setSpeed()
Added Wire.stretchClock() method for I2C clock stretching
Merge pull request #284 from spark/feature/i2c-dma-implementation

TwoWire Rework - added missing Slave mode using DMA/Interrupts and updated Master mode using DMA