Added RSA key file support

[ggruening]

Hello everybody,

some applications (like mysql for example) need key files in RSA format. I prepared RSA key conversion using openssl. You can enable it by setting CONVERT_KEY2RSA=yes.
If you think this is useful I'd update the README, too.

Best regards, and thanks for this fantastic tool.

Gregor

[kereis]

Hey, thank you for your contribution.

I have 2 suggestions:

1. Renaming CONVERT_KEY2RSA to CONVERT_KEY_TO_RSA.
2. As the new flag will affect all keys involved in the extraction process, we should consider renaming it into CONVERT_KEYS_TO_RSA (with KEYS having a plural 's')

[ggruening]

I gladly took up your suggestions, see my second commit.

[kereis]

Thank you for applying the suggestions. 👍

Another change that I have to request: #78 was merged recently which introduces a new way of specifying file names and extensions for both certificate and private key file. So you may adjust convert_keys_to_rsa() accordingly. See my review comments.

[ggruening]

Hey ho, I did it similar to #78, should be consistent again.

[kereis]

Thanks.

One tiny thing though: Can you add your new environment variables to the table of README.md? Afterwards, we can go ahead and merge your changes.

[ggruening]

I just added the new vars to the table of README.md. Furthermore I added an usage example. Hope this helps.

[kereis]

LGTM.

I will merge this one. Thank you for your contribution. 😄 👍

[ggruening]

You're welcome. Thanks again for your work. :)