Redesign exception hierarchy

All Mastodon.py errors now derive from MastodonError, for easier
catching in application code that just wants to see if something
happened, and isn't too miffed about the details.

I/O Errors derive from MastodonIOError, for similar reasons.

This change is designed to be backwards compatible.

docs/index.rst

@@ -112,12 +112,17 @@ Error handling
 When Mastodon.py encounters an error, it will raise an exception, generally with
 some text included to tell you what went wrong. 
 
+The base class that all mastodon exceptions inherit from is the MastodonError
+class. If you are only interested in the fact an error was raised somewhere in
+Mastodon.py, and not the details, this is the exception you can catch.
+
 MastodonIllegalArgumentError is generally a programming problem - you asked the 
 API to do something obviously invalid (i.e. specify a privacy scope that does
 not exist).
 
 MastodonFileNotFoundError and MastodonNetworkError are IO errors - could be you
-specified a wrong URL, could be the internet is down or your hard drive is dying.
+specified a wrong URL, could be the internet is down or your hard drive is
+dying. They inherit from MastodonIOError, for easy catching.
 
 MastodonAPIError is an error returned from the Mastodon instance - the server
 has decided it can't fullfill your request (i.e. you requested info on a user that

mastodon/Mastodon.py

@@ -1280,21 +1280,29 @@ class Mastodon:
 ##
 # Exceptions
 ##
-class MastodonIllegalArgumentError(ValueError):
+class MastodonError(Exception):
+    """Base class for Mastodon.py exceptions"""
+
+
+class MastodonIllegalArgumentError(ValueError, MastodonError):
     pass
 
 
-class MastodonFileNotFoundError(IOError):
+class MastodonIOError(IOError, MastodonError):
+    """Base class for Mastodon.py I/O errors"""
+
+
+class MastodonFileNotFoundError(MastodonIOError):
     pass
 
 
-class MastodonNetworkError(IOError):
+class MastodonNetworkError(MastodonIOError):
     pass
 
 
-class MastodonAPIError(Exception):
+class MastodonAPIError(MastodonError):
     pass
 
 
-class MastodonRatelimitError(Exception):
+class MastodonRatelimitError(MastodonError):
     pass