Make sure UART rx is active on bootup.
Reset RTS state to inactive when re-initializing UART.

This fixes the issues with flow our manual flow control implementation
described in #91.
Move baud rate to inside the UartDevice struct.
Wait after rebooting RN-42 to avoid locking it in an off state.

This may fix #135.
Match delay function with common type signature.
Move RN-4x initialization to a generic bluetooth namespace.
Move Bluetooth pin config to headers so they are included properly.