Add support for custom Ktlint RuleSets

[Karn]

A temporary branch for custom rules support while waiting for jeremymailen#279 to merge.

Usage:

buildscript {
  repositories {
    // ...
    maven { url "https://jitpack.io" }
  }
  
  dependencies {
    // ...
    classpath "io.karn:kotlinter-gradle:karn--enable-support-for-custom-rulesets-SNAPSHOT"
  }
}

If jitpack is down you can resolve via github:

buildscript {
  repositories {
    // ...
    maven {
      url "https://raw.githubusercontent.com/Karn/kotlinter-gradle/karn--enable-support-for-custom-rulesets-1/libs/"
      content {
        includeGroup("org.jmailen.gradle")
      }
    }
  }
  
  dependencies {
    // ...
    classpath "org.jmailen.gradle:kotlinter-gradle:3.12.0-local"
  }
}

Then add custom rulesets project

dependencies {
  // ...
  ktlintRuleset project(":build-ktlint-rules")
}