ENH/REF: Accept style args; use plot, not scatter.

FIX: Add missing line to respect user color choice.
Tweak extent to account for pixel centers.
REF: Do not use extent, just specify limits.
Warn on circle_size but translate it to markersize.
Merge pull request #155 from danielballan/improve-annotate

ENH/REF : Accept style args; use plot, not scatter.