RF+DOC: refactoring fiac example files

Fix various obvious import errors, document and rename.

[ci skip]
DOC: point to latest README for data release

We haven't released the data yet because we haven't resolved the
license. Point to the latest version of the README file on github for a
link, for now.
RF: cleanup + modernize imports for mayavi example
NF: add results comparison helper

This commit also records the regression testing I did against the
results of the ``fiac_example`` script from June 2009.

I ran the current ``fiac_example`` script against the same preprocessed
FIAC data, found on Fernando's machine.  The results from Fernando and
Jonathan's run of June 2009 were in the same directories.

There have been some extremely small precision changes in the NIPY code
since then due to changes in nibabel used for reading / writing images,
but these should not affect the results.

In order to make the current code replicate the previous results I had
to:

* Temporarily revert some (correct) more recent edits of the design code

    diff --git a/examples/fiac/fiac_example.py b/examples/fiac/fiac_example.py
    index c635287..cfb37f0 100644
    --- a/examples/fiac/fiac_example.py
    +++ b/examples/fiac/fiac_example.py
    @@ -55,7 +55,7 @@ def run_model(subj, run):
        # The TR of the experiment
        TR = 2.5
        # The time of the first volume
    -    Tstart = 0.0
    +    Tstart = 1.25
        # The array of times corresponding to each volume in the fMRI data
        volume_times = np.arange(nvol) * TR + Tstart
        # This recarray of times has one column named 't'.  It is used in the
    diff --git a/nipy/modalities/fmri/fmristat/hrf.py b/nipy/modalities/fmri/fmristat/hrf.py
    index e468dcb..02fe624 100644
    --- a/nipy/modalities/fmri/fmristat/hrf.py
    +++ b/nipy/modalities/fmri/fmristat/hrf.py
    @@ -57,7 +57,7 @@ def spectral_decomposition(hrf2decompose,
            TODO
        """
        if time is None:
    -        time = np.linspace(-15,50,3251)
    +        time = np.linspace(-15,50,3751)
        dt = time[1] - time[0]
        if delta is None:
            delta = np.arange(-4.5, 4.6, 0.1)

  This caused some small changes in precision only.

* allow for sign flip in image comparison

  The statistic images include tests on the second of two basis
  functions from the spectral set.  In 2009, this had a more or less
  random sign.  About a year ago I put a constraint on the sign (after
  discussing with Jonathan) so the sign need not be the same as the
  previous run of this analysis.

* Zero out the first two slices of the group mask

  There were some very low signal voxels at the bottom of the mask that
  were causing some numerical precision errors in the statistic images
  (but not the effect, sd images) for subject ``fiac_06``

* Reprocess subject ``fiac_03`` run 1 with TStart of 0

  It turned out that fiac_03 run 1 had been rerun a few days after the
  others, in 2009, with a Tstart (time of reference slice) of 0
  instead of the previous 1.25 (see above).

After these changes, the comparison script passes for all runs and
subjects.

During testing I sometimes went back to look at and run the code from
June 2009, specifically commit dc9d02b.
NF: add hashes for FIAC preprocessed data

To allow regression testing and to show the FIAC data file structure.
RF+TEST: refactor, fix, test isestimable function

``isestimable`` was using the wrong dimension for 1D vectors, and was
writing to ``shape``, thus modifying the input argument.  Add doctests
and tests.
BF: add back estimable check for FIAC example

``isestimable`` now fixed; add back estimable check for FIAC designs.
DOC: extend / format comments; rearrange code

For fiac_example

Should be no functional changes.
DOC: add comments and legends to FIR example

Note need for matplotlib
DOC: minor comments to parametric design example
DOC: adding comments, tests, explanations

to simple_contrast.py