[roll third_party/pigweed] docs: Add Google Developer Documentation Style

Take the first step of introducing the Google Developer Documentation
Style Guide into Pigweed's Doxygen and Sphinx style guides, and
eventually applying that to the rest of Pigweed. The GDDSG primarily
focuses on English language style rather than technical particulars
around e.g. Doxygen or RST.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/181112

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 5e701a80e68612c..ded10e4bc6d9313
Roller-URL: https://ci.chromium.org/b/8764249034827391809
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I1e79cf6f3b3fb0853630949f00050cd1c3464a0b
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/181273
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 5e701a8..ded10e4 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 5e701a80e68612c5dbb77da022e775151caaf0c1
+Subproject commit ded10e4bc6d931387dda61b637e40b6f3268e752