allow bookmaker methods to auto-populate

Adds
#Populate
as markup inside #Method, replacing
the method's description and #Param
and #Return. If present, this info
is retrieved from the include when
writing the web markdown and the
generated include.

TBR=caryclark@google.com

Docs-Preview: https://skia.org/?cl=162820
Bug: skia:
Change-Id: I5df16f227b86651d463e03ddd33849bb127891c0
Reviewed-on: https://skia-review.googlesource.com/c/162820
Commit-Queue: Cary Clark <caryclark@skia.org>
Auto-Submit: Cary Clark <caryclark@skia.org>
Reviewed-by: Cary Clark <caryclark@google.com>
Reviewed-by: Cary Clark <caryclark@skia.org>
10 files changed