Issue #118, generate pom.xml and sign build artifacts.

This is being done in preparation for publishing to maven central.

To ensure the ability to publish development versions of the library to
the local maven repository for developers that do not have the GPG keys
installed, we only attempt to sign the build artifacts when we are not
building a "-SNAPSHOT" version.

build.gradle

@@ -25,9 +25,9 @@ allprojects {
     }
 }
 
-
 subprojects {
-    version = '0.1.0'
+    group = 'org.partiql'
+    version = '0.1.0-SNAPSHOT'
 }
 
 buildDir = new File(rootProject.projectDir, "gradle-build/" + project.name)
@@ -49,7 +49,6 @@ configure(subprojects.findAll { it.name != 'example' }) {
     }
 }
 
-
 subprojects {
     plugins.withId('java', { _ ->
         sourceSets {

lang/build.gradle

@@ -21,10 +21,11 @@ plugins {
     id 'maven-publish'
     id 'org.jetbrains.kotlin.jvm'
     id 'io.gitlab.arturbosch.detekt'
+
+    id "signing"
 }
 
-version = '0.1.0'
-group = 'org.partiql.lang'
+
 
 tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
     kotlinOptions {
@@ -62,16 +63,70 @@ tasks.register('javadocJar', Jar) {
 
 publishing {
     publications {
-        create('maven', MavenPublication) {
-            artifactId = 'partiql-lang-kotlin'
+        maven(MavenPublication) {
+            // group id and version are set in the root build.gradle for all projects.
+            artifactId = "partiql-lang-kotlin"
 
-            from(components['java'])
-            artifact(tasks['sourcesJar'])
-            artifact(tasks['javadocJar'])
+            from components.java
+            artifact sourcesJar
+            artifact javadocJar
+
+            pom {
+                name = "PartiQL-Lang-Kotlin"
+                packaging = "jar"
+                url = "https://github.com/amzn/ion-schema-kotlin"
+                description = "An implementation of PartiQL for the JVM written in Kotlin."
+                scm {
+                    connection = "scm:git@github.com:partiql/partiql-lang-kotlin.git"
+                    developerConnection = "scm:git@github.com:partiql/partiql-lang-kotlin.git"
+                    url = "git@github.com:partiql/partiql-lang-kotlin.git"
+                }
+                licenses {
+                    license {
+                        name = "The Apache License, Version 2.0"
+                        url = "http://www.apache.org/licenses/LICENSE-2.0.txt"
+                    }
+                }
+                developers {
+                    developer {
+                        name = "Amazon Ion Team"
+                        email = "partiql-community@amazon.com"
+                        organization = "PartiQL"
+                        organizationUrl = "https://github.com/partiql"
+                    }
+                }
+            }
+        }
+    }
+    repositories {
+        maven {
+            url "https://oss.sonatype.org/service/local/staging/deploy/maven2"
+            credentials {
+                username ossrhUsername
+                password ossrhPassword
+            }
         }
     }
 }
 
+// The below enables developers and CI servers who do not have the GPG keys needed for signing to build locally,
+// while also signing release builds.
+// Signatures are only required when publishing to maven central anyway. We may need a more sophisticated means of
+// determining if we should sign the build artifacts someday, but this should suffice for now.
+if(!version.endsWith("SNAPSHOT")) {
+    println("""
+*******************************************************************************
+Note: 
+
+The build artifacts will be signed because this is NOT a SNAPSHOT version. 
+Signing will fail if you have not configured a ~/.gradle/gradle.properties 
+file with the correct values.  
+*******************************************************************************
+""")
 
+    signing {
+        sign publishing.publications.maven
+    }
+}