Gnuplot-based plotting for PDL

Changes for 2.025 - 2024-04-20

• Split version checking from `use Alien::Gnuplot` line for easier downstream packaging. Fixes #98.
• fixes for Windows (#89)
• use terminal "dumb" if probing shows "unknown" (#66)
• fix numeric-only strings for legend (#100) - thanks @d-lamb for report
• fix plot3d array-ref handling (#87) - thanks @djerius for report
• fix gplot array-ref handling (#86) - thanks @djerius for report
• add multiplot_next to skip one plot (#85)
• add documentation to UTF-8 encode text labels etc (#74) - thanks @Zaki for report
• add {multiplot,plot,multiplot_next,end_multi}_generate methods which return Gnuplot commands equivalent plot would execute (#95)

Frequently asked questions about Perl

Changes for 5.20230701 - 2023-07-01T00:23:37Z

• Fix Unicode code point range in glossary (Felipe Gasper, #98)
• faq4: recommend fc() for string sorting, rather than lc() (brian d foy, #102)