Validate spec on generation by default (#251)

* Validate spec on generation by default

Adds a validation parameter to CodegenConfigurator, and passes through
options from CLI, Maven Plugin and Gradle Plugin to that property.

Default is to validate the spec during generation. If spec has errors,
we will output errors as well as warnings to the user.

Option can be disabled by passing false to validateSpec (Maven/Gradle)
or --validate-spec (CLI).

* Prepare version 3.1.1-SNAPSHOT

* fix version

* Use last prod version for the sample

* Update README.md

Fix

* [cli] Option parser does not support true/false for boolean options

modules/openapi-generator-maven-plugin/src/main/java/org/openapitools/codegen/plugin/CodeGenMojo.java

@@ -60,6 +60,9 @@ public class CodeGenMojo extends AbstractMojo {
 
     private static final Logger LOGGER = LoggerFactory.getLogger(CodeGenMojo.class);
 
+    @Parameter(name="validateSpec", required = false, defaultValue = "true")
+    private Boolean validateSpec;
+
     @Parameter(name = "verbose", required = false, defaultValue = "false")
     private boolean verbose;
 
@@ -348,6 +351,11 @@ public class CodeGenMojo extends AbstractMojo {
 
         configurator.setVerbose(verbose);
 
+        // now override with any specified parameters
+        if (validateSpec != null) {
+            configurator.setValidateSpec(validateSpec);
+        }
+
         if (skipOverwrite != null) {
             configurator.setSkipOverwrite(skipOverwrite);
         }