update test infrastructure

build.gradle

src/main/jastadd/backend/AbstractGrammar.jadd

src/main/java/org/jastadd/relast/compiler/Mustache.java

...ain/java/org/jastadd/relast/compiler/RelAstProcessor.java

src/test/java/org/jastadd/relast/tests/PreprocessorTest.java

src/test/resources/Comments/config.yaml

src/test/resources/Comments/in/CommentsA.relast

src/test/resources/MinimalGrammar/config.yaml

src/test/resources/MinimalGrammar/in/CommentInFront.relast

src/test/resources/MinimalGrammar/in/Example.relast

...ava/org/jastadd/relast/tests/RelAstProcessorTestBase.java

...s/java/org/jastadd/relast/tests/config/Configuration.java