Merge pull request #6 from Lagerregal/master

Add "modify" option to add, remove and replace attributes

Fixed deprecation warning

Upgrade to Swift 4.0

 Using a web site LDAP server to perform tests.

Fixing invalid setter issue.

Correcting Typos

Improving SPNEGO / MD5 Application

Updating GSSAPI testing script

Also adding a reference krb5.conf for the test script

Cleanup Documents

Testing Modify()

Preparing Basic SASL Supports for LDAP