Improve api name for the Clojure client

For example, when an operation's tag is "users-api", "users_api" or
"UsersApi", generate the api file named users_api.clj and "users-api"
as the namespace (it was "usersapi.clj" and "usersapi" before).

To implement this, I have to move the "sanitizeTag" method from
DefaultGenerator.java to DefaultCodegen.java so that its behaviour can
be overridden in ClojureClientCodegen.java, which is needed as the
default implementation would sanitize "users-api" to "usersapi" before
the tag is passed to "toApiName" and "toApiFilename".

modules/swagger-codegen/src/test/java/io/swagger/codegen/languages/ClojureClientCodegenTest.java

@@ -0,0 +1,38 @@
+package io.swagger.codegen.languages;
+
+import org.testng.Assert;
+import org.testng.annotations.Test;
+
+public class ClojureClientCodegenTest {
+    ClojureClientCodegen codegen = new ClojureClientCodegen();
+
+    @Test
+    public void testSanitizeTag() throws Exception {
+        Assert.assertEquals(codegen.sanitizeTag("users-api"), "users_api");
+        Assert.assertEquals(codegen.sanitizeTag("users_api"), "users_api");
+        Assert.assertEquals(codegen.sanitizeTag("users api"), "users_api");
+        Assert.assertEquals(codegen.sanitizeTag("users.api"), "users_api");
+        Assert.assertEquals(codegen.sanitizeTag("Users Api"), "Users_Api");
+        Assert.assertEquals(codegen.sanitizeTag("UsersApi"), "UsersApi");
+        Assert.assertEquals(codegen.sanitizeTag("usersapi"), "usersapi");
+        Assert.assertEquals(codegen.sanitizeTag("Usersapi"), "Usersapi");
+    }
+
+    @Test
+    public void testToApiName() throws Exception {
+        Assert.assertEquals(codegen.toApiName("users_api"), "users-api");
+        Assert.assertEquals(codegen.toApiName("Users_Api"), "users-api");
+        Assert.assertEquals(codegen.toApiName("UsersApi"), "users-api");
+        Assert.assertEquals(codegen.toApiName("usersapi"), "usersapi");
+        Assert.assertEquals(codegen.toApiName("Usersapi"), "usersapi");
+    }
+
+    @Test
+    public void testToApiFilename() throws Exception {
+        Assert.assertEquals(codegen.toApiFilename("users_api"), "users_api");
+        Assert.assertEquals(codegen.toApiFilename("Users_Api"), "users_api");
+        Assert.assertEquals(codegen.toApiFilename("UsersApi"), "users_api");
+        Assert.assertEquals(codegen.toApiFilename("usersapi"), "usersapi");
+        Assert.assertEquals(codegen.toApiFilename("Usersapi"), "usersapi");
+    }
+}