Improve HISTORY and add AUTHORS.

Improve HISTORY and add AUTHORS.
In particular, mention the 4.0BSD and v8/Tahoe APIs that were
supported until OpenBSD 5.4 and that matter for the evolution
of RE functions in the BSD libc.

Joint work with and OK jsg@.

Regarding authorship of the v8 functions, Russ Cox writes
near the end of https://swtch.com/~rsc/regexp/regexp1.html :
"While writing the text editor sam in the early 1980s, Rob Pike
wrote a new regular expression implementation, which Dave Presotto
extracted into a library that appeared in the Eighth Edition.
Pike's implementation incorporated submatch tracking into an efficient
NFA simulation but, like the rest of the Eighth Edition source, was
not widely distributed.  Pike himself did not realize that his
technique was anything new.
Henry Spencer reimplemented the Eighth Edition library interface
from scratch, but using backtracking, and released his implementation
into the public domain.  It became very widely used, eventually
serving as the basis for the slow regular expression implementations
mentioned earlier: Perl, PCRE, Python, and so on.  (In his defense,
Spencer knew the routines could be slow, and he didn't know that a
more efficient algorithm existed.  He even warned in the documentation,
"Many users have found the speed perfectly adequate, although
replacing the insides of egrep with this code would be a mistake.")
Pike's regular expression implementation, extended to support
Unicode, was made freely available with sam in late 1992, but the
particularly efficient regular expression search algorithm went
unnoticed."  [...]