Add segment_outline option

[krassowski]

This gives better contrast when using non-black color for points and connectors.

upset(
    movies, genres, min_size=10,
    matrix=intersection_matrix(
        segment_outline=0.9,
        segment=geom_segment(color='#e15759'),
        outline_color=list(active="black", inactive="grey70"),
    ) + scale_color_manual(
        values=c('TRUE'='#e15759', 'FALSE'='grey'),
        na.value='transparent',
        guide='none'
    )
)