Add FILE_LICENCE declarations to almost all files that make up the
various standard builds of gPXE.

Given any block cipher, a corresponding CBC mode of behaviour for the
cipher can be created using the CBC_CIPHER() macro.

It is a programming error, not a runtime error, if we attempt to use
block ciphers with an incorrect blocksize, so use an assert() rather
than an error status return.

The various types of cryptographic algorithm are fundamentally
different, and it was probably a mistake to try to handle them via a
single common type.

pubkey_algorithm is a placeholder type for now.

Although the nature of the hack is essentially unchanged, this allows
us to remove the hardcoded assumption in tls.c that the RX cipher is
AES.

Use our own, more robust, ASN.1 parsing routines to extract the RSA
public key from a server certificate.  Remove the now-unused AXTLS
ASN.1 parser.

Allow initiator to verify target authentication using CHAP.

wasn't meant for my local "master" branch ;)
This reverts commit 373022108b.