add json tests; code cleanup;

fslstats.cc

tests/fslstats/feedsRun

tests/fslstats/test_cogMM_c.json

tests/fslstats/test_cogVox_C.json

tests/fslstats/test_diff_d_imageForDiff.nii.gz_m.json

tests/fslstats/test_entropyNonzero_E.json

tests/fslstats/test_entropy_e.json

tests/fslstats/test_histLimits_H_10_0_1.json

tests/fslstats/test_hist_h_10.json

tests/fslstats/test_maxCoord_x.json

tests/fslstats/test_meanHistCog_m_h_10_c.json

tests/fslstats/test_meanHist_m_h_10.json

tests/fslstats/test_meanNonzero_M.json

tests/fslstats/test_mean_m.json

tests/fslstats/test_mean_m_a.json

tests/fslstats/test_mean_m_a_n.json

tests/fslstats/test_minCoord_X.json

tests/fslstats/test_notRobust_R.json

tests/fslstats/test_percentileNonzero_P_50.json

tests/fslstats/test_percentile_p_50.json