Use UTF-8 encoding for docs and bump version to v0.18.0

Author: TobiGr

build.gradle

@@ -5,7 +5,7 @@ allprojects {
     sourceCompatibility = 1.7
     targetCompatibility = 1.7
 
-    version 'v0.13.0'
+    version 'v0.18.0'
     group 'com.github.TeamNewPipe'
 
     repositories {
@@ -43,7 +43,8 @@ task aggregatedJavadocs(type: Javadoc, group: 'Documentation') {
     title = "$project.name $version"
     // options.memberLevel = JavadocMemberLevel.PRIVATE
     options.links 'https://docs.oracle.com/javase/7/docs/api/'
-    
+    options.encoding 'UTF-8'
+
     subprojects.each { project ->
         project.tasks.withType(Javadoc).each { javadocTask ->
             source += javadocTask.source