docs with more pop

Replace a hunk of documentation in docs/*.bmh
with #Populate, which instructs bookmaker to
retrieve the documentation from include/core.

Check spelling for all documentation retrieved
from include/core against Skia declarations
and a list of words in spelling.txt.

TBR=caryclark@google.com
Docs-Preview: https://skia.org/?cl=163491
Bug: skia:
Change-Id: If057c3a1336e312ad59c084a3a130f0276802496
Reviewed-on: https://skia-review.googlesource.com/c/163491
Commit-Queue: Cary Clark <caryclark@skia.org>
Reviewed-by: Cary Clark <caryclark@skia.org>
Auto-Submit: Cary Clark <caryclark@skia.org>
54 files changed