man: separate out ncplot functions

doc/man/man3/notcurses_plot.3.md

@@ -37,18 +37,23 @@ typedef struct ncplot_options {
 ```
 
 **struct ncuplot* ncuplot_create(struct ncplane* n, const ncplot_options* opts, uint64_t miny, uint64_t maxy);**
+
 **struct ncdplot* ncdplot_create(struct ncplane* n, const ncplot_options* opts, double miny, double maxy);**
 
 **struct ncplane* ncuplot_plane(struct ncuplot* n);**
+
 **struct ncplane* ncdplot_plane(struct ncdplot* n);**
 
 **int ncuplot_add_sample(struct ncuplot* n, uint64_t x, uint64_t y);**
+
 **int ncdplot_add_sample(struct ncdplot* n, uint64_t x, double y);**
 
 **int ncuplot_set_sample(struct ncuplot* n, uint64_t x, uint64_t y);**
+
 **int ncdplot_set_sample(struct ncdplot* n, uint64_t x, double y);**
 
 **void ncuplot_destroy(struct ncuplot* n);**
+
 **void ncdplot_destroy(struct ncdplot* n);**
 
 # DESCRIPTION