support for serial read/write buffer (#384)

docs/reference/serial/read-buffer.md

@@ -0,0 +1,12 @@
+# Serial Read Buffer
+
+Read the buffered serial data as a buffer
+
+```sig
+serial.readBuffer(64);
+```
+
+### Returns
+
+* a Buffer containing input from the serial port. Empty if no data available.
+

docs/reference/serial/write-buffer.md

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+# Serial Write Buffer
+
+Write a buffer to the [serial](/device/serial) port.
+
+```sig
+serial.writeBuffer(pins.createBuffer(0));
+```
+
+### Parameters
+
+* `buffer` is the buffer to write to the serial port