"Host task" chapter desing

[PetroBondar]

Currently, the Host tasks chapter is not represented in the Reference Guide.

We propose to add it with the following structure:

• Host task
  • Host task basic concept (4.10.1. Overview)
  • sycl::interop_handle (4.10.2. Class interop_handle)
  • Additions to the sycl::handler class (4.10.3. Additions to the handler class)

This chapter will be added between the "Expressing Parallelism" and "Error Handling" chapters in the current structure:

Could you please review and provide your opinion and recommendations for this chapter?
We will create PR after a discussion.

[mkinsner]

This sounds good to me.

[PetroBondar]

Thanks for the comment!
Created PR: #131