API + ENH: more consistent attr/ param names, memorize all attrs

- memorize use_n_pca_components
COSMITS: remove duplicate doc
DOC: restructure reference section

- made thematic groups with headings
- ordered them alphabetically
DOC: reference structure

FIX: read_reject_parameters -> File I/O
DOC: reference structure

- ADD read and write functions to other sections
- RM mne.Covariance from FIle I/O
DOC: reference structure description
DOC: reference structure

sort alphabetically
DOC reference

remove `mne` prefix from classes
STY: Getting rid of warning on test
COSMITS II
DOC: reference structure

add modules names
DOC: reference structure

reorder chronologically, add "Covariance" section
DOC: reference structure

- subsume Projections under Preprocessing
- update intro
ENH?:

Added some section headings, also changes some names.
Merge pull request #328 from Eric89GXL/nose-clean-mxne

STY: Getting rid of warning on test
COSMITS III
Merge pull request #2 from dengemann/DOC

ENH?: Added some section headings, also changes some names. 
DOC: reference fix & consistency
DOC: reference

- Make location explicit
- headings: "sensor space data" and "source space data"
DOC: reference

move some functions