Sampler pi and month array values

[benswick]

In slope_sampler_pi_samples_array the last element is { 10.0 * G_PI, "20π" } but the text should be "10π".

Should the last slope_sampler_month_samples_array element for December be "Dec"? Some languages abbreviate it Dez but they also abbreviate other months differently than English. I couldn't find a language that only abbreviates December differently.

[elvismt]

Thanks for openin this issue @benswick. These labels are currently hard coded when they shoud be dynamically generated and localized. Unfortunatelly, I am busy like crazy these days with my PhD thesis :( so I'll probably not gonna touch it for a while. Feel free to modify this code.