VectorBus - add methods to handle non message events

[zariiii9003]

Add methods to handle vector driver events that are not caused by incoming messages. Can be implemented by subclassing.

I do not know if the docstrings are okay. sphinx-build doc/ doc/_build causes an error at reading sources... [ 16%] bus:
AttributeError: 'property' object has no attribute 'expandtabs'

[codecov]

Codecov Report

Merging #708 into develop will increase coverage by 0.12%.
The diff coverage is 77.77%.

@@             Coverage Diff             @@
##           develop     #708      +/-   ##
===========================================
+ Coverage    68.44%   68.57%   +0.12%     
===========================================
  Files           69       69              
  Lines         6218     6227       +9     
===========================================
+ Hits          4256     4270      +14     
+ Misses        1962     1957       -5

[christiansandberg]

Since the methods are to be used outside of the library they should not be internal, i.e. remove the underscore from the beginning of the names.

[zariiii9003]

Hello Christian,
the methods are not really meant to be called from outside. They are called from within _recv_internal.
The user has to implement the methods though. Would you remove the underscore anyway?

[christiansandberg]

If they start with an underscore there is no guarantee that they will be called in future versions, which might break applications relying on their existence. If they are public, they need to be treated according to semantic versioning meaning backwards incompatible changes may only be introduced in a new major version.