Tools: add parser to extract event definitions in source & generate json output

Example definition:
			/* EVENT
			 * @description
			 * test description
			 * @arg1: test
			 */
			events::send<uint8_t>(events::ID("test_event"),
					"test message", events::Log::Error, 0);

Tools/px4events/srcscanner.py

@@ -0,0 +1,52 @@
+import os
+import re
+import codecs
+import sys
+
+class SourceScanner(object):
+    """
+    Traverses directory tree, reads all source files, and passes their contents
+    to the Parser.
+    """
+
+    def ScanDir(self, srcdirs, parser):
+        """
+        Scans provided path and passes all found contents to the parser using
+        parser.Parse method.
+        """
+        extensions = tuple([".cpp"])
+        for srcdir in srcdirs:
+            if os.path.isfile(srcdir):
+                if not self.ScanFile(srcdir, parser):
+                    return False
+            else:
+                for dirname, dirnames, filenames in os.walk(srcdir):
+                    for filename in filenames:
+                        if filename.endswith(extensions):
+                            path = os.path.join(dirname, filename)
+                            try:
+                                if not self.ScanFile(path, parser):
+                                    return False
+                            except:
+                                print(("Exception in file %s" % path))
+                                raise
+        return True
+
+    def ScanFile(self, path, parser):
+        """
+        Scans provided file and passes its contents to the parser using
+        parser.Parse method.
+        """
+
+        with codecs.open(path, 'r', 'utf-8') as f:
+            try:
+                contents = f.read()
+            except:
+                contents = ''
+                print('Failed reading file: %s, skipping content.' % path)
+                pass
+        try:
+            return parser.Parse(contents)
+        except Exception as e:
+            print("Exception while parsing file {}".format(path))
+            raise