Feature/Refactor go to kotlin (#15)

* refactor sign from go to kotlin

* add withdrawal example

* update

add jni benchmark

add java example

* fix

Author: boyan01

library/build.gradle

@@ -15,7 +15,6 @@ configurations {
 }
 
 dependencies {
-    implementation fileTree(include: ['*.jar'], dir: 'libs')
     implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlinVersion"
     implementation "com.squareup.okhttp3:okhttp:$okhttpVersion"
     implementation "com.squareup.okhttp3:logging-interceptor:$okhttpVersion"