remove negative indices from neighbors cython code
  - use X.ndim - k instead of -k for indexing
MAINT charset is deprecated in favor of encoding

closes #2107
ENH add return_path in orthogonal matching pursuit

DOC Clarify docstrings
TEST for omp path feature
ENH OrthogonalMatchingPursuitCV estimator

FIX: work with max_iter=1, though it does not make sense

DOC add OrthogonalMatchingPursuitCV docstrings
DOC : docstring fixes
DOC : more docstring fixes
use pre_fit in OMP
API : deprecate a lot of extra parameters in OMP object
API : deprecations in orthogonal_mp
ENH : update example of OMP
FIX respect conventions in OMP init
update what's new + classes.rst
TST added tests for encoding/charset deprecation

Checking the old interface still works.
Merge pull request #2230 from pprett/neighbors-segfault-fix

Neighbors segfault fix
DOC better deprecation warning messages.

The charset parameter has been replaced by encoding and the charset_error by
decode_error.
TST catch deprecation warning in feature_extraction.text
Merge branch 'pr/2246'

MAINT charset is deprecated in favor of encoding