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.gradle

@@ -10,15 +10,15 @@ apply plugin: 'idea'
 
 jar {
     baseName = 'jdnssec-tools'
-    version =  '0.16'
+    version =  '0.17'
 }
 
 repositories {
     mavenCentral()
 }
 
-sourceCompatibility = 1.7
-targetCompatibility = 1.7
+sourceCompatibility = 1.8
+targetCompatibility = 1.8
 
 dependencies {
     compile fileTree(dir: 'lib', include: '*.jar')