[ENH] Consider to integrate new fieldmapless distortion correction method

[xiaosonghe]

There's a new development in fieldmapless distortion correction that utilize deep learning to build a b0 map from T1 data: https://www.biorxiv.org/content/10.1101/2020.01.19.911784v1 Here's the Github page for the package: https://github.com/MASILab/Synb0-DISCO It seems promising and hopefully it can perform better than the current "experimental" version.

[smeisler]

Of note, it is being integrated in DIPY 0.17.0 release, should make integration easier.