ENH allow empty grid in ParameterGrid

Fixes #2048.
DOC fix some docstring/parameter list mismatches

Particularly in metrics and linear_model.bayes.
See #2062 for a list and a script to fetch them.
DOC ParameterGrid on lists

Thanks to @mblondel for explaining this functionality.
Merge pull request #2082 from larsmans/empty-parameter-grid

MRG allow empty grid in ParameterGrid
FIX avoid spectral_embedding naming conflict
FIX : missing y=None in FactorAnalysis
Merge pull request #2085 from agramfort/fix_y_score_fa

FIX : missing y=None in FactorAnalysis
Add missing doc string printing for examples
Merge pull request #2087 from ahojnnes/examples-print-doc

Add missing doc string printing for examples
renamed weight to sample_weight in sklearn/isotonic.py
Merge pull request #2090 from kanielc/fix_weight

MAINT renamed weight to sample_weight in sklearn/isotonic.py
FIX: make doc auto-linking support any Unicode / UTF-8 content
Make the out-of-core example plot work when launched by the sphinx extension
COSMIT move deprecated parameter to end

Thanks @agramfort for pointing this out