Serialport Support

- allow communication to elm327 device via a serialport
- allow creation of elm327 device without requiring unwrap()
- added some extra documentation
- expose reset() functionality of device
- serial_comm and ftdi_comm abstractions added

src/device/ftdi_comm.rs

@@ -0,0 +1,42 @@
+use super::serial_comm::{SerialComm, DEFAULT_BAUD_RATE};
+use super::Result;
+use std::io::{Read, Write};
+
+/// Communicate with a USB to Serial FTDI device
+/// with the FTDI library
+pub struct FTDIDevice {
+    device: ftdi::Device,
+}
+
+impl FTDIDevice {
+    /// Creates a new instance of an FTDIDevice
+    pub fn new() -> Result<Self> {
+        let mut device = ftdi::find_by_vid_pid(0x0404, 0x6001)
+            .interface(ftdi::Interface::A)
+            .open()?;
+
+        device.set_baud_rate(DEFAULT_BAUD_RATE)?;
+        device.configure(ftdi::Bits::Eight, ftdi::StopBits::One, ftdi::Parity::None)?;
+        device.usb_reset()?;
+
+        Ok(Self { device })
+    }
+}
+
+impl SerialComm for FTDIDevice {
+    fn write_all(&mut self, data: &[u8]) -> Result<()> {
+        Ok(self.device.write_all(data)?)
+    }
+
+    fn read(&mut self, data: &mut [u8]) -> Result<usize> {
+        Ok(self.device.read(data)?)
+    }
+
+    fn set_baud_rate(&mut self, baud_rate: u32) -> Result<()> {
+        Ok(self.device.set_baud_rate(baud_rate)?)
+    }
+
+    fn purge_buffers(&mut self) -> Result<()> {
+        Ok(self.device.usb_purge_buffers()?)
+    }
+}