Gradle API Scanner plugin (#1669)

* Skeleton plugin.
* Implement Gradle api-scanner plugin, and apply it.
* Generate API documentation for any jar without a classifier.
* Fix usage of smokeTests classifier.
* Tweak Gradle API usage.
* Upgrade to fast-classpath-scanner 2.7.0
* Include interfaces and more modifiers in the class description.
* Allow system classes to be supertypes and implemented interfaces.
* Make API Scanner plugin configuration tweakable via build.gradle.
* Add a miserable amount of unit testing.
* Sort methods and fields using their natural comparators. Way easier!
* Add README for api-scanner plugin.
* Add @OutputFiles to ScanApiTask.
* Rename ScanApiTask to ScanApi.
* Allow the ScanApi task to be disabled.
* WIP: Create a top-level GenerateApi task to collate the ScanApi output.
* Exclude package-private classes, as well as bridge/synthetic methods.
* Replace "End of Class" delimiter with '##'.
* Don't scan modules whose API is still "in flux".
* Include constructors in the API definitions.
* Finish implementation of GenerateApi task.
* Update README to include GenerateApi task.
* Filter out Kotlin's "internal" methods.
* Assign "fatjar" classifier to the fat jar artifact.
* Enhance README for GenerateApi.
* Explain effect of api-scanner plugin, and link to Corda's API strategy.
* Tweak README
* Exclude synthetic Kotlin classes by analysing @Metadata.
* Allow us to exclude some classes explicitly from the API.

node/src/smoke-test/kotlin/net/corda/node/CordappSmokeTest.kt

@@ -42,7 +42,7 @@ class CordappSmokeTest {
         val pluginsDir = (factory.baseDirectory(aliceConfig) / "plugins").createDirectories()
         // Find the jar file for the smoke tests of this module
         val selfCordapp = Paths.get("build", "libs").list {
-            it.filter { "-smoke-test" in it.toString() }.toList().single()
+            it.filter { "-smokeTests" in it.toString() }.toList().single()
         }
         selfCordapp.copyToDirectory(pluginsDir)