Resolve "Allow collection and circular attributes as endpoint targets"

Closes #53 (closed)

• Check, if collection and circular attributes can be specified as send endpoint targets.
• Add test cases to ensure correct handling.
• Update documentation, that they can be used.

ragconnect.base/build.gradle

@@ -187,12 +187,20 @@ ext {
 }
 application.mainClassName = "${mainClassName}"
 
+def parametersTxtFileName = 'ragconnect.base/parameters.txt'
 task runParameters(type: JavaExec) {
+    doFirst {
+        if (!new File(parametersTxtFileName).exists()) {
+            throw new GradleException("Please create '${parametersTxtFileName}' to use this task.")
+        }
+    }
     group 'application'
     description 'Run using parameters.txt (line-separated with comments)'
     classpath sourceSets.main.runtimeClasspath
     main = "org.jastadd.ragconnect.compiler.Compiler"
-    args new File('ragconnect.base/parameters.txt').text.strip().split("\n").dropWhile { it.startsWith("#") }
+    try {
+        args new File(parametersTxtFileName).text.strip().split("\n").dropWhile { it.startsWith("#") }
+    } catch (FileNotFoundException ignored) { /* empty */ }
     standardInput = System.in
 }