Error handling

[Pessimistress]

For #4134

Change List

• Do not throw during layer lifecycles: initialize, update, finalize, draw
• Switch error logging from log.warn to log.error
• Add onError callback to Deck class (see updated documentation)
• Test

[coveralls]

Coverage decreased (-0.03%) to 83.355% when pulling 6a588be on x/error-handling into c4aae05 on master.

[tsherif]

Seems like a sensible change.

Long term, I wonder if we could do something like Vulkan's validation layers: https://vulkan-tutorial.com/Drawing_a_triangle/Setup/Validation_layers#page_What-are-validation-layers

The basic idea is Vulkan by default doesn't do any kind of error checking, but you can add these layers when instantiating it that instrument the core functions with various error checks. It would potentially allow us to include more esoteric debug functionality (e.g. Seer support) without weighing down core classes.

[Pessimistress]

@tsherif We do something similar with props validation, based on the debug flag. We could potentially default debug to true in non-production mode?