Check every word in docs

This enables checking all text to see if it
either represents a valid reference or is a
word in docs/spelling.txt . Expressions are
checked for validity as well.

There are a few shortcuts (marked with TODO):
- typedefs aren't resolved, so cheats are
added for SkVector and SkIVector.
- operator overload detection is incomplete
- constructor detection is incomplete
- formula definitions aren't detected

Found and fixed a bunch of spelling, usage,
and incorrect or obsolete references.

A few comment changes are needed in
include/core to get this to work, mostly
centered around recent SkPaint/SkFont edits.

TBR=reed@google.com
Docs-Preview: https://skia.org/?cl=167541
Bug: skia:
Change-Id: I2e0d5990105c5a8482b0c0d3e50fd0b330996dd6
Reviewed-on: https://skia-review.googlesource.com/c/167541
Reviewed-by: Cary Clark <caryclark@skia.org>
Auto-Submit: Cary Clark <caryclark@skia.org>
Commit-Queue: Cary Clark <caryclark@skia.org>
diff --git a/docs/SkIRect_Reference.bmh b/docs/SkIRect_Reference.bmh
index 3bbfd68..b308f53 100644
--- a/docs/SkIRect_Reference.bmh
+++ b/docs/SkIRect_Reference.bmh
@@ -828,7 +828,7 @@
 
 IRects intersect when they enclose a common area. To intersect, each of the pair
 must describe area; fLeft is less than fRight, and fTop is less than fBottom;
-empty() returns false. The intersection of IRect pair can be described by:
+SkIRect::isEmpty() returns false. The intersection of IRect pair can be described by:
 #Formula # (max(a.fLeft, b.fLeft), max(a.fTop, b.fTop),
             min(a.fRight, b.fRight), min(a.fBottom, b.fBottom)) ##.