fix `_computescale(scale::typeof(mean), x, y)` (#55)
fix `_computescale(scale::typeof(mean), x, y)` (#55)

do not weigh distances of points with themselves if `x==y`
heliosdrm/RecurrenceAnalysis.jl,heliosdrm/RecurrenceAnalysis.jl,heliosdrm/RecurrenceAnalysis.jl