[bugfix] variance smoothing in batch mode

Variance smoothing was not taken into account in batch mode due to wrong
spelling for "vFWHM"
[new] Batch two sample t-test (nominal)

Batch version of two-sample t-test nominal version (i.e. no covariate,
no variance smoothing, no approximate test).
[bugfix] Interactive two sample t-test (nominal)

Modified interactive version of nominal two-sample t-test (no covariate,
no variance smoothing, no approximate tests) is now working and provided
the same results as before.
[gitconfig] Ignore asv files

Configure Git so that it ignores files with "asv" extensions.