[HarfBuzz] Some questions for the documentation

[Khaled Hosny]

Hi,

I’m trying to document all of buffer functions [1], and somethings are
no very clear to me.

* What is the purpose of hb_buffer_get_empty() and how is it different
  from hb_buffer_create()?

* What is the implications of using different cluster levels?
  My understanding is that level 0 merges clusters of combining marks to
  their bases, any thing else? And what is the difference between level
  1 and two?

Regards,
Khaled

1. http://behdad.github.io/harfbuzz/harfbuzz-Buffers.html