style: Fix PEP8 blank lines issues in Python files

Done with `autopep8 --select=E3,W3`, fixes:

- E301 - Add missing blank line.
- E302 - Add missing 2 blank lines.
- E303 - Remove extra blank lines.
- E304 - Remove blank line following function decorator.
- E309 - Add missing blank line.
- W391 - Remove trailing blank lines.

doc/tools/doc_merge.py

@@ -16,6 +16,7 @@ tab = 0
 
 old_classes = {}
 
+
 def write_string(_f, text, newline=True):
     for t in range(tab):
         _f.write("\t")
@@ -23,6 +24,7 @@ def write_string(_f, text, newline=True):
     if (newline):
         _f.write("\n")
 
+
 def escape(ret):
     ret = ret.replace("&", "&");
     ret = ret.replace("<", "&gt;");
@@ -36,6 +38,7 @@ def inc_tab():
     global tab
     tab += 1
 
+
 def dec_tab():
     global tab
     tab -= 1
@@ -43,12 +46,14 @@ def dec_tab():
 write_string(f, '<?xml version="1.0" encoding="UTF-8" ?>')
 write_string(f, '<doc version="' + new_doc.attrib["version"] + '">')
 
+
 def get_tag(node, name):
     tag = ""
     if (name in node.attrib):
         tag = ' ' + name + '="' + escape(node.attrib[name]) + '" '
     return tag
 
+
 def find_method_descr(old_class, name):
 
     methods = old_class.find("methods")
@@ -61,6 +66,7 @@ def find_method_descr(old_class, name):
 
     return None
 
+
 def find_signal_descr(old_class, name):
 
     signals = old_class.find("signals")
@@ -73,6 +79,7 @@ def find_signal_descr(old_class, name):
 
     return None
 
+
 def find_constant_descr(old_class, name):
 
     if (old_class == None):
@@ -85,6 +92,7 @@ def find_constant_descr(old_class, name):
                     return m.text
     return None
 
+
 def write_class(c):
     class_name = c.attrib["name"]
     print("Parsing Class: " + class_name)
@@ -93,7 +101,6 @@ def write_class(c):
     else:
         old_class = None
 
-
     category = get_tag(c, "category")
     inherits = get_tag(c, "inherits")
     write_string(f, '<class name="' + class_name + '" ' + category + inherits + '>')
@@ -106,7 +113,6 @@ def write_class(c):
         if (old_brief_descr != None):
             write_string(f, escape(old_brief_descr.text.strip()))
 
-
     write_string(f, "</brief_description>")
 
     write_string(f, "<description>")
@@ -207,5 +213,3 @@ for c in list(old_doc):
 for c in list(new_doc):
     write_class(c)
 write_string(f, '</doc>\n')
-
-