OPT: Modified dipy.core.sphere_stats.random_uniform_on_sphere, see issue 181.
BF: Changed from numpy.hstack to numpy.vstack as suggested by MrBago.
DOC: Added a 'Notes' and a 'References' section to dipy.core.sphere_stats.random_uniform_on_sphere, as per Numpy/Scipy documentation style guidelines.
Merge pull request #183 from ecaruyer/fix-for-issue-181

OPT: Modified dipy.core.sphere_stats.random_uniform_on_sphere, cf issue #181