Support top level statements

* A great feature is added into Pythran: scripts outside of functions can also
  be compiled.
* These top level statements are taken into __init__. Then the __init__ is
  loaded into the cxx boost.
Remove arch target from default flags

it messes up with -DUSE_BOOST_SIMD
Add test case for top-level statement support

* Since top-level statement can not be treated in a normal way, its' test cases
  are added into INTERNAL.rst
* test_doc.py is also adjusted so that the command lines in INTERNAL.rst can be
  executed
Add support for dtype in arange

And a few test cases!
Support array indexing through an array for any numpy expression
Fix several memory leaks

When initializing an ndarray from a pointer, do not automatically set
the memory as foreign. Do it only if asked too, i.e. if the memory comes
from Python.
Improve numpy array filtering

- only allocate an index buffer instead of a full ndarray
- works for assignment too
- now pass the periodic_dist test case
Fix implementation of zeroes_like and ones_like in SIMD context
Add partial support for numpy.copyto

This makes it possible to pass a new test case from stackoverflow.
Pythran performs slightly worst than parakeet on this test case :-$.
Merge pull request #157 from yuancheng2013/top_level_support

Support top level statements
Merge pull request #190 from serge-sans-paille/copyto

Copyto
Merge pull request #188 from serge-sans-paille/filter-write

Improve numpy array filtering
Add Pythran logo

SVG version, enthusiastically chosen by Pythraners, with a CC license
and the original copyright respected.
Merge pull request #187 from serge-sans-paille/logo

Add Pythran logo
Split pythonic into several headers

The main goal of this work was to decrease compilation time, which is a
success, clang can now run the full test suite more than 4 times faster
that it used to.

The new layout is briefly explained in doc/DEVGUIDE.rst.

Additionally, some issues were fixed as part of the new pythonic
validation process:

- Fix issue in indexed_array constructor (bad type forwarding leading to deep copy)
- Remove g++4.8 workaround (including only the relevant header decreases
  its memory consumption, so that the workaround is no longer mandatory)
- Fix nditerator dangling reference issue
- Test some functions that were never tested
- Prune functions that were never implemented
- Update Pythonic doc

Overall, I am very happy with that commit. My only regret is that the
commit history is lost, so let's thanks a lot Pierrick for his work on
numpy (and his contributions to that commit too!), Alan for itertools,
Adrien for str and xmar for his work on operators.
Lazy evaluation of single assigned numpy expression
Add good code for lazy analysis
Add log to numpy
Specialize bitwise nan operation for boolean
Lazy typing for conditional statements