Added agent authentication
Added docs for agent authentication
Fix unlink(); now uses the correct function

ssh2_sftp_unlink() is the correct function to unlink a file, not ssh2_sftp_symlink()
Use arguments passed into connect method.
Merge pull request #12 from camspiers/connect-arguments-fix

Use arguments passed into connect method.
Merge pull request #10 from awildeep/sftp-unlink-fix

Fix unlink(); now uses the correct function
Merge pull request #7 from camspiers/agent-auth

Agent auth