Jinja Templates

Re-write Nbconvert using Jinja Template. 

It Is **much more easier** to tweek and to make inheriting template, 
without having to code a class that inherit from Converter.py

look at `converter/converter_template.py`
and 
`templates/*.tpl`

I considere `templates/python.tpl` almost done, and which fixes some 
strangeness of previous implementation that had inconsistencies in blank lines. 

usage 

`./nbconvert2.py profile ipynb_file`

generating a diff with current ipynb references: 

```
diff -U3  tests/ipynbref/IntroNumPy.orig.html <(./nbconvert2.py profile ipynb_file)
```

I would really like the though of @ellisonbg, @fperez.
Pinging @damianavila  which might be interested.

Todo : 
  - [x] write a preprocessor that extract files
  - [x] make the 'extrator' key configurable
  - [x] cleanup the makefile that generate jinja-tex template from jinja template
  - [x] create a kind of 'profile' which would contain the configuration for each 'format'
  - [x] make the filter/preprocessors 'Configurables'
  - [x] write preprocessor worksheet/cell/output decorator to simplify the task
  - [x] write RST converter
  - [x] write blogger converter
  - [x] document
  - [x] stabilize API
  - [x] check header delimiters : {1: '=', 2: '-', 3: '~', 4: '.', 5: '\'', 6: '`'}
  - [ ] write (more) test
  - [ ] write separated smaller test
  - [ ] replicate remove_math replace_math step in md2latex / other(?) converter



Maybe/Later PR
  - [x] integrate Damián Reveal converter
      - people interested in the same converter but to beamer.
  - [x] add coalesce stream preprocessor
  - [ ] write a preprocessor that inline files
  - [x] write Markdown converter
  - [ ] add a preprocessor that remove non prioritary display data for conversion speed lower memory footprint

To Fix :

  - [ ] output not monospace in output html
  - [ ] tex: `<obj>` rendered as  `¡obj¿`