First commit for a working flow control mod, the only handles flow control for incoming right now, and requires a dirty hack in the variant.h and variant.cpp files.

I'm planning on trying to refine it to not need the hacks.
I've tested this successfully at 115200 baud with large webpages.
Removed changes in variant.h completely and reduced changes needed in variant.cpp.

The USART0_Handler function in variant.cpp has to be commented out for this to work, I haven't found a way to change the handler for that IRQ yet.

Also, Implemented Stream with the DigiFi class, you can now do wifi.write(), wifi.available(), wifi.read() etc just like with the Serial classes.

Signed-off-by: ags131 <ashumann13@gmail.com>
Some minor renaming changes
Added setCTSPin(int) and changed setFlowControl to enableCTS(bool)
Fixed USARTClass.cpp so it actually uses ctsPin
Merge pull request #1 from ags131/FlowControl

Flow control