Error reporting

[leandrodamascena]

@mingrammer @gabriel-tessier

Related to #229.

Sometimes graphivz exe isn't installed, user don't read documentation in a appropriate way or even the diagrams tool might have a bug, and because of that the diagrams tool should have a more consistent error handler..

Of course we need to discuss about messages and exceptions, but I think it's a good improvement. :).

Look this prototype.

Using a decorator on exit ("with" implementation all execute init and exit). In this case I removed graphviz exe from my path and got a ExecutableNotFound exception

Using a decorator to on init . In this case I simulated a mistake and changed "name" to "nme" and got a TypeError exception

[gabriel-tessier]

@leandrodamascena
Look good it will help to figure out problems more easily!

[mingrammer]

This feature looks amazing. Thank you for work on it!

I have two suggestions for this.

1. Decorator name: In my thought, @exception decorator could make users confused that seems to throw an exception rather than catching the exceptions. So it would be good to change to a more meaningful name (less confusable) such as catch, report, or whatever.

2. Message format: What do you think about adding a name (key) for errors too in the message like Python and Platform?

Error:         TypeError
Python:        3.8.2...
Platform:      Windows...

[leandrodamascena]

@mingrammer @gabriel-tessier

Great that you both liked this. I need few days to prepare the code and make a PR, first I need to finish this gabriel-tessier/diagrams-web#1 and other things in other projects.

Before to push PR I paste here the prototype update.

Thank you guys!