Adds p.break_ for explicit newlines in lib.pretty

p.break_() explicitly includes a newline while pretty printing, and maintains indentation.
A simple test is included to show this working.
Uses p.break_() when repr() is used for printing

When a newline is found in the result of repr() (using the default printer), the newline is replaced with an appropriate call to p.break_()
enable cython highlight in notebook
remove executable flag on soem files
Split exporter in to for ipynb->ipynb
some trailing whitespace
import baseexporter in init
Exporter -> TemplateExporter / BaseExporter
fix 1 test
renamed:    exporter.py -> template_exporter.py
renamed:    baseexporter.py -> exporter.py
renamed:    template_exporter.py -> templateexporter.py
Rebase changes made by hand
Check if class is an instance of Exporter, not TemplateExporter
Fixed Travis, missing import in export.py
@MinRK fix suggestions
renamed:    test_exporter.py -> test_templateexporter.py
Added tests for nb2nb Exporter
Also fixed some small things in template exporter tests.
Added a lightweight "core" Makefile entry

`make core` now runs a lightweight doc build process that doesn't include the
"api" target. The "html" target now just references "core" and "api".

This patch is a candidate for backporting to 1.x.
Initial updates to magics re: `%load_ext`, etc.

Also copied over preamble from octavemagic doc regarding installation of
appropriate packages to other magics, and a note about installing R or Octave
separately where relevant.