Add cmdline doctests for AFNI.

- Remove example_data() call in Bandpass doctest.
- Add several skipped run doctests.
- Remove unnecessary position requirements in FourierInputSpec,
TCorrelateInputSpec
- Add retrend argument to Fourier.
- Adding cmdline doctest to TCorrMap revealed that it’s breaking.
- Changed BrickStatInputSpec from AFNICommandInputSpec to
CommandLineInputSpec and BrickStat from AFNICommand to AFNICommandBase
because BrickStat returns a value instead of outputting a file. I
haven’t checked that aggregate_outputs actually returns the value.
- Fixed Eval doctest (was using Calc doctest).
- Fixed MaskTool doctest (was using Automask doctest).
- Changed TCat argument rlt from Str to Enum, since there are only
three possible options (rlt, rlt+, rlt++).

Author: tsalo