Add version command

Added support for a version command, which will output the tag version for encpass.sh and the SHA256 checksums (if sha256sum is available) for encpass.sh and any enabled extension.

$ encpass.sh version
tag version: v4.1.0
SHA256 Checksum: d4e57f32106a8820901b43cd6398e8a42f9df96010a3074d57bde7ffd0e781e7  /usr/local/bin/encpass.sh
SHA256 Checksum: 5f8a0bcad3033322f9ffbf78cf58d7f02ec599712a0d57e2f83690fc22d43ba6  /usr/local/bin/encpass-keybase.sh

The tag version corresponds to the git commit that is tagged with that same version number. It is possible that the script on your local could contain additional changes beyond that particular tag version (e.g. you pulled it directly from the master branch), but those changes would only at most go up to just before the next tag version number.

You can determine if your version of encpass.sh is identical to a specific commit or tag in the official repo by computing the SHA256 checksum of a particular commit of the encpass.sh script. To find the SHA256 checksum of an encpass.sh commit or tag from the git repo, just curl the raw script to your local and pipe it into sha256sum:

curl --silent https://raw.githubusercontent.com/plyint/encpass.s/93d42340c24e62132049430dd26c26736697e440/encpass.sh | sha256sum