OpenSSL KeepOut .kpt header file support

[clach04]

See https://antofthy.gitlab.io/software/#keepout
From https://antofthy.gitlab.io/software/keepout.sh.txt

# Example header...
#
#   KeepOut
#   -aes-256-cbc
#   -md sha512
#   -iter 5067274
#   -pbkdf2
#   -salt
#   __DATA__
#
# Encryption defaults used by "keepout" (file magic, cipher, hashing digest,
# and pbkdf2 iteration count) can only be set inside the script, at this time.
# Changing these will not effect the scripts ability to decrypt existing
# 'keepout' files (that is the point after all).  The order of the options does
# not matter.
#
# After the '__DATA__' line (including a newline), is the "openssl enc" output
# generated using those options with the users password.  Note that the
# iteration count is also randomised, as a further 'salting' of the
# encryption.

Depends on #111 and clach04/openssl_enc_compat#2