CECPQ1 is a new key exchange that concatenates the results of an X25519
key agreement and a NEWHOPE key agreement.

Change-Id: Ib919bdc2e1f30f28bf80c4c18f6558017ea386bb
Reviewed-on: https://boringssl-review.googlesource.com/7962
Reviewed-by: David Benjamin <davidben@google.com>

obj_mac.h is missing #include guards, so one cannot use NIDs without
pulling in the OBJ_* functions which depend on the giant OID table. Give
it #include guards, tidy up the style slightly, and also rename it to
nid.h which is a much more reasonable name.

obj_mac.h is kept as a forwarding header as, despite it being a little
screwy, some code #includes it anyway.

BUG=chromium:499653

Change-Id: Iec0b3f186c02e208ff1f7437bf27ee3a5ad004b7
Reviewed-on: https://boringssl-review.googlesource.com/7562
Reviewed-by: Steven Valdez <svaldez@google.com>
Reviewed-by: David Benjamin <davidben@google.com>