Mocked out DatabaseEntry in case sqlalchemy is not installed
Removed unnecessary import, reinserted sot test
Add a document describing how to contribute code to SunPy.

This will be shown upon creation of new issues and Pull Requests:
https://github.com/blog/1184-contributing-guidelines
Grammar
Added a test for mock DatabaseEntry if sqlalchemy is not present
Include dummy test even when sqlalchemy is present
Added changelog entry
Removed dummy test
added link to Astropy coding standards in dev documentation
Merge pull request #947 from Cadair/contributing

Add a document describing how to contribute code to SunPy.
Merge pull request #945 from amras1/remove-sqlalchemy-map

[Review]: Removed sqlalchemy requirement from map_factory
Merge pull request #948 from dpshelio/devguide

Astropy Coding standard linked in our dev documentation
Merge pull request #949 from Cadair/master

[BugFix]: Coveralls tweaks