WIP: adding utils module for code support

[matthew-brett]

Add utils.py module for general code support, with to_scalar function to start the ball rolling.

[coveralls]

Coverage increased (+0.002%) to 96.212% when pulling 43746b1 on matthew-brett:add-utils-module into 3d59146 on nipy:master.

[codecov-io]

Codecov Report

Merging #530 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #530      +/-   ##
==========================================
+ Coverage   94.25%   94.25%   +<.01%     
==========================================
  Files         177      179       +2     
  Lines       24273    24289      +16     
  Branches     2604     2606       +2     
==========================================
+ Hits        22878    22894      +16     
  Misses        920      920              
  Partials      475      475

Impacted Files	Coverage Δ
nibabel/tests/test_utils.py	100% <100%> (ø)
nibabel/utils.py	100% <100%> (ø)

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