RFE: RFC7512 URI support

[dwmw2]

https://github.com/stefanberger/go-pkcs11uri adds support for parsing and handling PKCS#11 URIs, but we could do with better integration. In particular, matching tokens and objects against criteria given in a URI.

In https://github.com/dwmw2/rolesanywhere-credential-helper/blob/pkcs11/aws_signing_helper/pkcs11_signer.go I've had to implement functions like matchSlots to return the slots matching a given URI, and getFindTemplate to build a FindObjects template from the URI. These would better as first-class citizens rather than each application needing to implement them.

[dwmw2]

Ah, perhaps this is a duplicate of #129

I think better integration of the URI code would be beneficial; having it merely available as a wrapper isn't ideal.

[miekg]

looks to me like those functions need to be available in go-pkcs11uri