[Diff since v0.15.4](https://github.com/lanl-ansi/PowerModels.jl/compare/v0.15.4...v0.15.5)


**Closed issues:**
- Best Output Behavior of Bus Phase Angles, when the model has no such variable (#6)
- Unit Tests for Matpower Parser Error Messages (#41)
- Documentation of Multi-Conductor (#281)
- Remove pg_sqr variables from conic formulations (#353)
- Robustness of constraint_thermal_limit with lowerbounds (#399)
- Review Solution Collection Time (#478)
- Solution builder fails on components with status=1 and their bus_status = 4 (#606)

**Merged pull requests:**
- Fixes for PWL Cost Functions in Matpower Tools (#687) (@ccoffrin)
- Remove Flow Variables from PF Definition (#688) (@ccoffrin)
- NLSolve AC Power Flow Solver (#689) (@ccoffrin)
- Minor Fix to the Mathematical Model Docs (#690) (@ccoffrin)
- Use Generic InfrastructureModels Tools (#691) (@ccoffrin)
- Update PWL Implementation to Extreme-Point Variant (#692) (@ccoffrin)
- Fix some docstrings (#693) (@raphaelsaavedra)
- Breaking Updates to Data Helper Functions (#694) (@ccoffrin)
- Improved Generator Assignment in AC-PF (#695) (@ccoffrin)