Merge pull request odlgroup#504 from odlgroup/odl040

REL: create 0.4.0 release notes

REL: bump version to 0.3.1

Merge pull request odlgroup#441 from odlgroup/issue-336__move_odlpp

Issue 336  move odlpp

Merge pull request odlgroup#469 from odlgroup/issue-463__phantoms_folder

API: move phantoms to new odl.phantoms dir

DOC: make PRs file a pure include file without structure

REL: fix minimum version of pytest

MAINT: set version to 0.2.1 in setup.py

ENH: add 'conj' method to FunctionSpaceVector

ODL release 0.1, core feature complete