Several documentation enhancements and build warnings fixes

- Made the documentation even more friendly towards newbies.
- Eased the usage of methods like get history which now set
  a default empty message for message actions and vice versa.
- Fixed some docstring documentations too.
- Updated the old normal docs/ to link back and forth RTD.
- Fixed the version of the documentation, now auto-loaded.

readthedocs/conf.py

@@ -20,6 +20,11 @@
 # import os
 # import sys
 # sys.path.insert(0, os.path.abspath('.'))
+import os
+import re
+
+
+root = os.path.abspath(os.path.join(__file__, os.path.pardir, os.path.pardir))
 
 
 # -- General configuration ------------------------------------------------
@@ -55,9 +60,12 @@ author = 'Lonami'
 # built documents.
 #
 # The short X.Y version.
-version = '0.15'
+with open(os.path.join(root, 'telethon', 'version.py')) as f:
+    version = re.search(r"^__version__\s+=\s+'(.*)'$",
+                        f.read(), flags=re.MULTILINE).group(1)
+
 # The full version, including alpha/beta/rc tags.
-release = '0.15.5'
+release = version
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.