Update test.py --task speed and study (#2099)

* Add --speed benchmark

* test range 256 - 1536

* update

* update

* update

* update

utils/plots.py

@@ -223,7 +223,7 @@ def plot_targets_txt():  # from utils.plots import *; plot_targets_txt()
     plt.savefig('targets.jpg', dpi=200)
 
 
-def plot_study_txt(path='study/', x=None):  # from utils.plots import *; plot_study_txt()
+def plot_study_txt(path='', x=None):  # from utils.plots import *; plot_study_txt()
     # Plot study.txt generated by test.py
     fig, ax = plt.subplots(2, 4, figsize=(10, 6), tight_layout=True)
     ax = ax.ravel()