USART module: write integer as string

Added methods to write integer values to USART:
* USARTx_Write_Int()            //   0,   1,  22, 333, 4444
* USARTx_Write_Int_FixedWidth() // 000, 001, 022, 333, 4444
ADC DMA module: add initial module implementation

* Read ADC channels into memory using DMA.
* Add example: read ADC and write data to USART.