Merge pull request #573 from Hypnus1803/patch-1

Update plotting.rst
make the relations entry<->FITS header entries and entry<->FITS key comments non-bidirectional
fixed test
Database.download: do not connect to a VSO server if an unknown kwarg is passed
added another pytest `slow` mark
Merge pull request #567 from Cadair/0.3_0.3.1

Bugs in 0.3.0
bump version numbers
Merge pull request #575 from Cadair/0.3

bump version numbers
Merge branch '0.3'
Merge branch 'master' of https://github.com/sunpy/sunpy into database
added attrs module to database reference
added short description of database package in docstring of sunpy package
added database guide
added database guide link to TOC of guides
updated database/TODO.rst
removed unused pytest fixture
updated database/TODO.rst again, lot of cleaning up
again, updated database/TODO.rst
Fixed links in plotting guide. This fixes issue #576.
Updated example code in README.md. This fixes issue #570.