[tor-bugs] #6357 [Stem]: Stem's exception classes should be moved to the module's top level

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#6357: Stem's exception classes should be moved to the module's top level
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 Reporter:  neena   |          Owner:  neena
     Type:  task    |         Status:  new  
 Priority:  normal  |      Milestone:       
Component:  Stem    |        Version:       
 Keywords:          |         Parent:       
   Points:          |   Actualpoints:       
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 Stem's controller library part currently defines & raises some exceptions
 all of which are defined in the submodule stem.socket.

 While it made sense to have them there while the only exceptions that were
 raised were SocketClosed & SocketError, now that it includes a more non-
 socket related exceptions than socket related ones I think it makes sense
 to move them to the module's top level. (Things like InvalidRequest &
 InvalidArguments).

 If we're doing this, I can make the changes along with my controller class
 modifications.

 (stem.socket.InvalidRequest would become stem.InvalidRequest and so on.)

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/6357>
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