GeanyLua: Add geany.range.

[Skif-off]

Maybe remove

if (start < 0) { return FAIL_UNSIGNED_ARG(1); }
if (stop < 0) { return FAIL_UNSIGNED_ARG(2); }

?

[Skif-off]

@xiota, @b4n, @eht16, @elextr , Winnie-the-Pooh and all-all-all :)

Scintilla uses SCI_GETTEXTRANGE with the Sci_TextRange structure, so we have no way to access the text without using the selection functions, but that can be inconvenient in some cases.