added command to generate documentations locally

This merge request added a new group of commands ("local") to "bdt" command which allows to run the functionalities implemented for CI to run locally. For the moment this group only has "docs" command to generate documents of bob/beat packages locally.

fixes partially #19 (closed)

bob/devtools/scripts/ci.py

@@ -651,9 +651,14 @@ def docs(ctx, requirement, dry_run):
   """Prepares documentation build
 
   This command:
+    \b
+    
     1. Clones all the necessary packages necessary to build the bob/beat
        documentation
+    \b       
+       
     2. Generates the `extra-intersphinx.txt` and `nitpick-exceptions.txt` file
+    \b    
 
   This command is supposed to be run **instead** of `bdt ci build...`