Migrate to Gradle (#1159)

* Start gradle root

* Clean up test API ambiguities

These don't compile in gradle anymore and the team[] warns

* Exclude .gradle dirs in git

* Set up moshi module

* Set up moshi-adapters

* Add repositories to subprojects

* Set target/source compatibility

* Set up examples

* Fix location of reflect/test dir

* Set up moshi-kotlin

* Set up code gen

* Opportunistic update code gen deps

* Fix up with code gen

* Set up kotlin tests

* Update snapshots

* Update travis build

* Configure checkstyle

* Cache gradle

* Finish fixing up checkstyle

* Now disable checkstyle until we can fix them all :|

* Update contributing

* Fix tests in codegen

* Remove unnecessary annotation

* Remove maven stuff!

* Suppress warning

* Remove jcenter

* Consolidate dependencies

* Revert "Clean up test API ambiguities"

This reverts commit 3ead69b844b5d7f66134b721e95581f5df1cccd6.

* Fix incap dep

* Opportunistically fix some small kotlinpoet deprecations

* Automatically apply the stdlib to all kotlin projects

* Opportunistic move to opt-in and remove unnecessary annotations

The kotlin maven plugin didn't handle these well in the IDE, gradle does

* Fix Type doc warning

* Fix okio version

* Fix dokka support

* Fix copypasta

* Use new snapshot

* Kotlin 1.4.0

buildSrc/src/main/kotlin/Dependencies.kt

@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) 2020 Square, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+object Dependencies {
+
+  const val asm = "org.ow2.asm:asm:7.1"
+  const val jsr305 = "com.google.code.findbugs:jsr305:3.0.2"
+  const val okio = "com.squareup.okio:okio:1.16.0"
+  const val okio2 = "com.squareup.okio:okio:2.1.0"
+
+  object AutoService {
+    private const val version = "1.0-rc7"
+    const val annotations = "com.google.auto.service:auto-service-annotations:$version"
+    const val processor = "com.google.auto.service:auto-service:$version"
+  }
+
+  object Incap {
+    private const val version = "0.3"
+    const val annotations = "net.ltgt.gradle.incap:incap:$version"
+    const val processor = "net.ltgt.gradle.incap:incap-processor:$version"
+  }
+
+  object Kotlin {
+    const val version = "1.4.0"
+    const val stdlib = "org.jetbrains.kotlin:kotlin-stdlib:$version"
+    const val metadata = "org.jetbrains.kotlinx:kotlinx-metadata-jvm:0.1.0"
+  }
+
+  object KotlinPoet {
+    private const val version = "1.6.0"
+    const val kotlinPoet = "com.squareup:kotlinpoet:$version"
+    const val metadata = "com.squareup:kotlinpoet-metadata-specs:$version"
+    const val metadataSpecs = "com.squareup:kotlinpoet-metadata-specs:$version"
+    const val elementsClassInspector = "com.squareup:kotlinpoet-classinspector-elements:$version"
+  }
+
+  object Testing {
+    const val assertj = "org.assertj:assertj-core:3.11.1"
+    const val compileTesting = "com.github.tschuchortdev:kotlin-compile-testing:1.2.8"
+    const val junit = "junit:junit:4.12"
+    const val truth = "com.google.truth:truth:1.0"
+  }
+}