Style guide tweaks.

I think this is better wording for function documentation. Also note that C++
code uses Google C++ naming rather than OpenSSL, per
c273d2c537dcd4b66e5235dab14cc7d6e983fc09.

Change-Id: I7334296bf1490395b2ba02e8b6ce245635826df2
Reviewed-on: https://boringssl-review.googlesource.com/3500
Reviewed-by: Adam Langley <agl@google.com>