v0.2.3

FBCModelTests v0.2.3

Diff since v0.2.2

Closed issues:

• use Base.@kwdef for setting up defaults for constant-holding structures (#51)

Merged pull requests:

• Add @kwdef to constructors (#64) (@stelmo)
• implement a small OMEX packer (#65) (@exaexa)
• finally fix the flux-in-variability check (#66) (@exaexa)