Merge pull request #1284 from oemof/release/v0.6

Release/v0.6

Merge pull request #1262 from oemof/release/v0.6

Release/v0.6.3

Merge pull request #1251 from oemof/release/v0.6

Release v0.6.2

Merge pull request #1239 from oemof/features/streamline-results-api

Merge streamlining the `Results` API into `dev`

Merge pull request #1231 from oemof/fix/inconsistency-custom-attribut…

…es-properties

Harmonise usage of "custom_..." keywords

Release v0.6.1

Merge pull request #1228 from oemof/release/v0.6

Release v0.6.1a2

Lists latest beta release of oemof.network as requirement.

Release v0.6.0

Package v0.6.0rc1

Reformat license information