Add doxygen checker (#1540)

* Fixed Doxygen issues
 * Updated Doxygen config
 * Added new script to test whether doxygen generation was successful or not
 * Added to Travis CI

JerryScript-DCO-1.0-Signed-off-by: László Langó llango.u-szeged@partner.samsung.com

tools/check-doxygen.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+
+# Copyright JS Foundation and other contributors, http://js.foundation
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+echo -n "Generating documentation with doxygen ..."
+DOXYGEN_WARNINGS=$((doxygen > /dev/null) 2>&1)
+echo " finished"
+
+if [ -n "$DOXYGEN_WARNINGS" ]
+then
+  echo "$DOXYGEN_WARNINGS"
+  exit 1
+fi