Missing Apache source headers

[hyandell]

I noticed the following files were missing Apache headers.

./error/s2n_errno.c
./error/s2n_errno.h
./tls/s2n_cbc.c

Happy to add them. I don't have private repos setup for my account, so didn't do a PR.

I've got the change done and 'make' succeeded. Didn't want to commit without your okay.

[hyandell]

Also noticing no LICENSE/NOTICE files. Happy to dig them up and add if you give the nod.

[colmmacc]

Sounds good! Please do commit. I should add a "make license" target to include the license in every file if it isn't already.

Incidentally, if you fork a private repo, the fork stays private even though it's in your account and you're on a free plan. forks of private paid-for repos are grandfathered in, probably for enterprise security reasons.

[hyandell]

Ah - didn't know that :) I'll go ahead and do it the pull-request way.