Fold the kotlin-codegen-runtime into Moshi itself.

Rename @MoshiSerializable to @JsonClass. Like @Json, I'm anticipating
a future where there are other interesting properties on this annotation.
Perhaps a future feature where Moshi is strict and only adapts types that
have a '@JsonClass' annotation.

Also rename MoshiKotlinCodeGenProcessor to JsonClassCodeGenProcessor. We
may later support other ways of generating code here; perhaps for regular
Java types.

pom.xml

@@ -24,7 +24,6 @@
     <module>kotlin</module>
     <module>kotlin-codegen/compiler</module>
     <module>kotlin-codegen/integration-test</module>
-    <module>kotlin-codegen/runtime</module>
   </modules>
 
   <properties>