Docstring wordings, refactored /r/me handling, updated README.

rtv/exceptions.py

@@ -1,23 +1,31 @@
-class SubmissionError(Exception):
-    """Submission could not be loaded"""
+class EscapeInterrupt(Exception):
+    "Signal that the ESC key has been pressed"
+
+
+class RTVError(Exception):
+    "Base RTV error class"
+
+
+class AccountError(RTVError):
+    "Could not access user account"
+
+
+class SubmissionError(RTVError):
+    "Submission could not be loaded"
 
     def __init__(self, url):
         self.url = url
 
 
-class SubredditError(Exception):
-    """Subreddit could not be reached"""
+class SubredditError(RTVError):
+    "Subreddit could not be reached"
 
     def __init__(self, name):
         self.name = name
 
 
-class ProgramError(Exception):
-    """Problem executing an external program"""
+class ProgramError(RTVError):
+    "Problem executing an external program"
 
     def __init__(self, name):
         self.name = name
-
-
-class EscapeInterrupt(Exception):
-    """Signal that the ESC key has been pressed"""