DWI::SDeconv: support direct response function input as vector of coefs

Allows the response function coefficients to be provided as a list of
comma-separated values, or as a file. The application will try to parse
the list as a vector a values first, and load the file if that fails.
DWI::Shells: update to option documentation
Fix compilation warning due to returning NAN instead of int
New command 'warpinit'

Provides replacement for 0.2 'gen_unit_warp' command.