"match" subcommand to check key<->crt match

[frdmn]

[frdmn]

/cc @snedr

[frdmn]

Depends on https://github.com/frdmn/openssl-cert-tools/issues/5

[frdmn]

Not sure if this is actually necessary. It would require the user to specify two input files from file system.

In this case, the user could easily just run the actual openssl md5 commands to check and compare the hashes:

openssl x509 -noout -modulus -in frd.mn.crt | openssl md5
openssl rsa -noout -modulus -in frd.mn.key | openssl md5
openssl req -noout -modulus -in frd.mn.csr | openssl md5