integrate 'construct' python library

'construct' is a declarative symmetric encoder/decoder for user
specified binary formats.  It should come in extremely handy in
tools like pySim.

We start the integration by adding transport methods for transceiving
APDUs with built-in encoding of the command data and decoding of the
response data.

Change-Id: Ibf457aa8b9480a8db5979defcfafd67674303f6c

docs/library.rst

@@ -73,6 +73,14 @@ at 9600 bps.  These readers are sometimes called `Phoenix`.
 .. automodule:: pySim.transport.serial
    :members:
 
+
+pySim construct utilities
+-------------------------
+
+.. automodule:: pySim.construct
+   :members:
+
+
 pySim utility functions
 -----------------------