Tools/px_process_module_doc.py: add script to extract documentation

And turn it into a markdown page.
It also does some simple validation, to check that the getopt() arguments
match the documentation.

Tools/px4moduledoc/srcscanner.py

@@ -0,0 +1,46 @@
+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", ".c"])
+        for srcdir in srcdirs:
+            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.
+        """
+        prefix = "^(|.*" + os.path.sep + ")src" + os.path.sep
+        scope = re.sub(prefix.replace("\\", "/"), "", os.path.dirname(os.path.relpath(path)).replace("\\", "/"))
+
+        with codecs.open(path, 'r', 'utf-8') as f:
+            try:
+                contents = f.read()
+            except:
+                contents = ''
+                print('Failed reading file: %s, skipping content.' % path)
+                pass
+        return parser.Parse(scope, contents)