Do not load notebook plugin by default

The notebook plugin is no longer loaded by default.
In particular the files `vimnb.vim` and `vimnb_call.sh` do not need to in the
vim plugin path. Currently the setup is as follows:

 * `vimnb` must be executable, in your path.
	In it, there is a variable `FILEDIR`, that must be set to the path of
	the directory containing all other files.
 * `pywrap.py` must be executable in the `FILEDIR` directory
 * In `vimnb.vimrc` the path to `FILEDIR` is hardcoded. Change to your
	situation.
 * `vimnb` will load `vimnb.vimrc`, which in turn will source the usual vimrc
	files (in `/etc`, and in your home directory). It will also source the
	`vimnb.vim` plugin from (and this is hardcoded, see previous point) the
	`FILEDIR` directory.
Add some rudimentary codeblock manipulations
Adds better functionality to codeblock textobjects

We have codeblock textobjects (b).
So:
 - Xab (X eg in {cdvy}) will change/delete/select/yank an outer block
	#{{{ through #}}}
 - Xib will X an inner block, really only the python code.
	(line after #{{{) through (line before #> --- or #}}})
 - Xio will X the output (#> --- through the line before #}}})

Moreover, [b, ]b, [B, ]B move between begin and end of codeblocks.
Adds color rules for output from the Python REPL
Adds keyboard shortcuts for executing codeblocks

Adds some comments on the go
Removes hardcoded paths

The only hardcoded path is now `FILEDIR` in the shell file vimnb