v1.12.0

PowerSystems v1.12.0

Diff since v1.11.2

Merged pull requests:

• Update README.md (#802) (@pitmonticone)
• Update index.md (#803) (@pitmonticone)
• Update intro_page.md (#804) (@pitmonticone)
• Update type_structure.md (#805) (@pitmonticone)
• Update system.md (#806) (@pitmonticone)
• Update time_series.md (#807) (@pitmonticone)
• Update network_matrices.jl (#808) (@pitmonticone)
• merge doc patch prs (#809) (@jd-lara)
• Cb/update pm parsers (#810) (@claytonpbarrows)
• Add check_components method (#811) (@daniel-thom)
• Fix time_periods in Modeling with JuMP (#813) (@odow)