v0.5.6

Alpine v0.5.6

Diff since v0.5.5

Merged pull requests:

• Implement DualStatus (#236) (@blegat)
• Fix documentation build (#237) (@odow)
• Implement RawStatusString (#238) (@blegat)

Closed issues:

• Is minlp_solver a required field? (#232)
• Confused about the problems supported in Alpine (#233)
• README misprint (#235)