add windows builder

Add windows builder and move to setup-go@v2 as it
supports adding GOPATH/bin to PATH without quirks.

Signed-off-by: Tobias Kohlbau <[email protected]>

piv: document that attestation certificate must not be used for tls

piv: add test that Certificate() returns ErrNotFound

piv: fix slot object IDs and add management key slot

*: update import path

*: remove gitignore