v0.3.1

SolverTools v0.3.1

Diff since v0.3.0

Closed issues:

• Add empty values in logs (#151)

Merged pull requests:

• CompatHelper: bump compat for "JLD2" to "0.2" (#147) (@github-actions[bot])
• add objgrad and objgrad! in LineModel (#148) (@tmigot)
• add citation (#149) (@geoffroyleconte)
• travis -> actions, update README (#150) (@dpo)
• change doc badge readme (#152) (@tmigot)
• Allow missing values in log_row (#154) (@abelsiqueira)
• Support DataFrames 0.22 (#155) (@mohamed82008)