Review FSL eddy interface

Just fixed PEP8 errors in the interface and reviewed the solution
for the bugs, that were already solved.

Please, close #769.
Merge branch 'master' into bug/fixEddyWrapper

Conflicts:
	nipype/interfaces/fsl/epi.py
fix typo
Merge pull request #907 from oesteban/bug/fnirtfileutils

fix typo in WarpUtils input traits
ENH: tidy up fsl-epi tools

* TOPUP: regarding #794, #796 I've cleaned up the docstring and implemented
  the three arguments that were still missing. The problem is that TOPUP
  admits one or more values for them, so the implementation of all the
  traits should be updated.

* Eddy: the implementation of @JensNRAD seems to work out, I reviewed
  the docstring. Close #769.

* Added deprecation notices and minor fixes.
pep8
Merge pull request #909 from oesteban/fix/TidyFSL-EPI

Tidy fsl epi interfaces
Update .travis.yml
ENH: N4BiasFieldCorrection new arguments

Now, it is possible to save the estimated bias field, by fully supporting
the --output argument specification.
added metadata to input trait in N4BiasFieldCorrection

Both comments satisfied (https://github.com/nipy/nipype/pull/911#discussion_r16982315)
Merge pull request #911 from oesteban/enh/N4-output-bias

ENH: N4BiasFieldCorrection new arguments
Added epi_reg interface
add to init, cosmetic changes
New interface TkRegister2
Minor edits in resampling interfaces
Adding positional information to ApplyWarp interface
Fix bbregister init-reg argument
auto_tests
add to init and changes, rename some arguments and add descriptions, add
example
create automatic test