ENH: Add above_threshold_color option to dendrograms.
TST: Check dendrogram plot with alternate colors.
BLD: fix a number of Bento build warnings.

c_misc was first added to includes for all modules, not just when needed.

Also update .gitignore for missing generated _ellip_harm_2.h file.

[ci skip]
DOC: document scipy.optimize.RootResults attributes
Merge pull request #4202 from QuLogic/dendrogram-threshold-color

Dendrogram threshold color
Merge pull request #4207 from andyfaff/rootresults

DOC: document scipy.optimize.RootResults attributes
Merge pull request #4205 from rgommers/fix-cmisc-warnings

BLD: fix a number of Bento build warnings.