Add support for ed25519 private keys in pkcs8

[teutat3s]

Picking up the great work from @arekinath in #83. This PR is identical to #83 apart from one change to fix the mentioneed style issue mentioned in #83 (comment).

Feel free to cherry-pick / rebase this into the initial PR if you prefer.

Make check passes for me with this change:

make check
deps/javascriptlint/build/install/jsl --nologo --nosummary --conf=tools/jsl.node.conf lib/key.js lib/dhe.js lib/fingerprint.js lib/formats/ssh-private.js lib/formats/pkcs1.js lib/formats/openssh-cert.js lib/formats/putty.js lib/formats/x509-pem.js lib/formats/pem.js lib/formats/x509.js lib/formats/ssh.js lib/formats/pkcs8.js lib/formats/auto.js lib/formats/dnssec.js lib/formats/rfc4253.js lib/ed-compat.js lib/ssh-buffer.js lib/certificate.js lib/index.js lib/signature.js lib/errors.js lib/algs.js lib/private-key.js lib/identity.js lib/utils.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/key.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/dhe.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/fingerprint.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/formats/ssh-private.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/formats/pkcs1.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/formats/openssh-cert.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/formats/putty.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/formats/x509-pem.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/formats/pem.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/formats/x509.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/formats/ssh.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/formats/pkcs8.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/formats/auto.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/formats/dnssec.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/formats/rfc4253.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/ed-compat.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/ssh-buffer.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/certificate.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/index.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/signature.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/errors.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/algs.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/private-key.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/identity.js
/Users/teutat3s/Code/github.com/TritonDataCenter/node-sshpk/lib/utils.js
deps/jsstyle/jsstyle -f tools/jsstyle.conf lib/key.js lib/dhe.js lib/fingerprint.js lib/formats/ssh-private.js lib/formats/pkcs1.js lib/formats/openssh-cert.js lib/formats/putty.js lib/formats/x509-pem.js lib/formats/pem.js lib/formats/x509.js lib/formats/ssh.js lib/formats/pkcs8.js lib/formats/auto.js lib/formats/dnssec.js lib/formats/rfc4253.js lib/ed-compat.js lib/ssh-buffer.js lib/certificate.js lib/index.js lib/signature.js lib/errors.js lib/algs.js lib/private-key.js lib/identity.js lib/utils.js
check ok

Related to #81

[bahamat]

make check passes, and test suite passes on SmartOS:

1..681
# tests 681
# pass  681

# ok