Add more documentation to the classes/methods

* add type annotations in-line with PEP484
* convert existing documentation to follow the
  "Google Python Style Guide" format understood by
  the sphinx.ext.napoleon' extension
* add much more documentation all over the code base

Change-Id: I6ac88e0662cf3c56ae32d86d50b18a8b4150571a

pySim/exceptions.py

@@ -22,18 +22,27 @@
 #
 
 class NoCardError(Exception):
+	"""No card was found in the reader."""
 	pass
 
 class ProtocolError(Exception):
+	"""Some kind of protocol level error interfacing with the card."""
 	pass
 
 class ReaderError(Exception):
+	"""Some kind of general error with the card reader."""
 	pass
 
 class SwMatchError(Exception):
 	"""Raised when an operation specifies an expected SW but the actual SW from
 	   the card doesn't match."""
-	def __init__(self, sw_actual, sw_expected, rs=None):
+	def __init__(self, sw_actual:str, sw_expected:str, rs=None):
+		"""
+		Args:
+			sw_actual : the SW we actually received from the card (4 hex digits)
+			sw_expected : the SW we expected to receive from the card (4 hex digits)
+			rs : interpreter class to convert SW to string
+		"""
 		self.sw_actual = sw_actual
 		self.sw_expected = sw_expected
 		self.rs = rs