Error handling chapter desing

[PetroBondar]

Currently, the "Error Handling" chapter looks like this:

The proposed structure looks like this:

• Error handling
  • Error handling rules (4.13.1. Error handling rules)
  • Exceptions (4.13.2. Exception class interface)

PR with updates will be created soon. Feel free to comment if you have any suggestions on the structure.

[mkinsner]

I think it would be good to:

1. Raise the "async error handler" (https://registry.khronos.org/SYCL/specs/sycl-2020/html/sycl-2020.html#subsubsec:exception.async) section to the higher level
2. Move the exceptions section to be first to be the first sub-section

With these changes the outline would look like:

• Error handling
  • Exceptions (4.13.2. Exception class interface)
  • Asynchronous error handler (4.13.1.1. Asynchronous error handler)
  • Error handling rules (4.13.1. Error handling rules)

[PetroBondar]

Thanks for the comment! It sounds good to me.
I'll update it this way.

[PetroBondar]

PR with renewed skeleton: #115