RF: Consolidate attribute assigning in Searchlight's result_fx

With different result_fx implementations that shape and content of
attributes can be totally different, so all this should consistent
with the actual result_fx
ENH: Extend pass_attr feature to support additional use cases

Like:
- renaming
- axes swapping
- explicit target attribute collections

fully backward compatible
RF: Split _postcall in Measures

This is necessary to allow for picking up the 'null_prob' CA in Node's
pass_attr facility.
ENH: add FlatSurfacePlotter to the suite
Merge branch 'master' of https://github.com/PyMVPA/PyMVPA
DOC: first update to Changelog preparing for 2.3.0 release. Note: so far only describes some changes by NNO. TODO: expand
ENH: add surf_caret, afni_niml_roi, afni_niml_annot to the suite
DOC: minor updates
NF: help function find_attribute_node to travel a NIML raw dataset tree easily
ENH: better parsing support for NIML raw dataset files, supporting mixed datatypes
ENH: remove warning message for when not all data can be converted to NIML; use a debug message instead
RF+ENH: also allow NIML datasets to have mixed datatypes (following the update on afni_niml)
ENH+RF+NF: rewrite of parsing NIML annotation files; write support for annotating files; support for merging annotation files
ENH: minor cleanup
DOC: added a couple of new packages to modref.rst. XXX these are still not included when running "make htmldoc" ?!
RF: rename datasets.niml_dset to datasets.niml
BF: fix import in suite
PL: minor spacing of code
DOC: niml dataset -- minor tune up + example of .. versionadded
BF: atlases -- adding missing enries to recently intoduced __all__