font doc

Prepping SkFont.h so that docs can be generated.
Mostly copying and pasting documentation with
edits to match SkFont conventions.

Added parameter names where missing to public
functions.

In a follow-on CL bookmaker will generate the
corresponding docs/SkFont_Reference.bmh

R=reed@google.com

Bug: skia:
Change-Id: Ib413b07000b368e2ee1b9145da1fca206a07a592
Reviewed-on: https://skia-review.googlesource.com/c/171646
Commit-Queue: Cary Clark <caryclark@google.com>
Reviewed-by: Mike Reed <reed@google.com>
2 files changed