Port to DNSJava 3.5.1, Java 8, linter fixes (#13)

* Initial port to dnsjava 3.5.1

* java.util.Date -> java.time.Instant
* for (Iterator ..) to for ( Object : List )
* DSRecord.<digest type> -> DNSSEC.Digest.<type>
* source to java 8

* formatting overhaul; copyright; author

* add slf4j jars for dnsjava 3.5.1

* NSEC/NSEC3 ttls are now min(soa.min, soa.ttl)

* Upgrade to commons-cli-1.5; some linter fixes

* Add CDS support of jdnssec-dstool

* linter suggestions

* add a TODO list

* Add a TODO list

build.xml

@@ -47,8 +47,8 @@
            deprecation="true"
            includeantruntime="false"
            includes="com/verisignlabs/dnssec/"
-           source="1.7"
-           target="1.7" />
+           source="8"
+           target="8" />
   </target>
 
   <target name="sectools-jar" depends="usage,sectools">