ENH: fast reads on large gzip files

Fixes #209
BUG: fix previous commit

Acutally use the opening logic
NF: add copy of OrderedDict for Python 2.6 compat

DICOM will need OrderedDict; copy in the external module until we
require Python 2.7
RF+TST: refactor _write_data utility routine

Add tests to check behavior with different shapes.  Add tests for
modifying data in-place.
RF: refactor check for nan_fill value

Take estimated error into account when checking whether nan2zero nan_fill
value is compatible with correct scaling to shared range of integer and
float.
DOC: add new formats to README / long description

Add notes of nifti2 / minc2 support.
Also add one-liner first line description for API docs.
BF: add optpkg fix for odd import error

This fix comes from dipy; it was in order to deal with cvxopt, but it's
probably sensible in general.
DOC: fix footnote ref in data package discussion
DOC: fix misc docstring formatting

Add /fix one-line descriptions of modules.

Fix bad formatting in lists in docstrings.

Fix misspelled docstring section headings.
DOC: switch to mathjax for math rendering

Makes the doc build faster; page load should also be quick because we
were using a lot of generated math PNG images.
RF: remove copy of sphinx autosummary

sphinx has this in version 0.6 (but it seems it was a little broken).
Version 1.0 released in 2010, so we should be safe now.
NF: add apigen stuff from dipy / skimage

Edited to make a little more general, and customize for nibabel.

Thanks Stefan vdW for keeping this working well.
RF: use apigen machinery for docs

Use dipy / sklearn machinery to generate the API docs.

Fixup `api.rst` to include some more modules, and add full API
reference.
DOC: add modules to API listing

Add some modules to API listing.
RF: use pip for pydicom install not easy_install

No need for easy_install
DOC: start documenting image API more
RF: stop API generation duplicating docstrings

Stop api generation tool generating docs for things that are not defined
in the module being documented.
DOC: add to the API topic lists
DOC: clean up docstrings for API docs

Clean up various RST formatting issues in docstrings to make the API
docs look nicer.
RF: documenting module objects as parameter

Add parameter to select skipping of objects not defined in the module
for documentation generator.