The cipher suite rules could also be anchored on SSL_TXT_* if desired. I
currently documented them in prose largely because SSL_TXT_* also
defines protocol version strings and those are weird; SSL_TXT_TLSV1_1
isn't even a cipher rule. (And, in fact, those are the only SSL_TXT_*
macros that we can't blindly remove. I found some code that #ifdef's the
version SSL_TXT_* macros to decide if version-locked SSL_METHODs are
available.)

Also they clutter the header. I was thinking maybe we should dump a lot
of the random constants into a separate undocumented header or perhaps
just unexport them.

I'm slightly torn on this though and could easily be convinced in the
other direction. (Playing devil's advocate, anchoring on SSL_TXT_* means
we're less likely to forget to document one so long as adding a
SSL_TXT_* macro is the convention.)

Change-Id: Ide2ae44db9d6d8f29c24943090c210da0108dc37
Reviewed-on: https://boringssl-review.googlesource.com/5962
Reviewed-by: Adam Langley <agl@google.com>