Note 8 - Stockholders' Equity - Warrants (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Outstanding, number of shares (in shares)	1,074,171	1,500,000	1,500,000
Outstanding, weighted average exercise price (in dollars per share)	$ 0.50	$ 2.55	$ 2.55
Outstanding, weighted average remaining life (Year)	3 years 310 days	2 years 343 days	4 years 36 days	354 days
Outstanding, intrinsic value			$ 956,012
Issued, number of shares (in shares)		1,749,171
Issued, weighted average exercise price (in dollars per share)		$ 0.50
Issued, weighted average remaining life (Year)		4 years 310 days
Issued, intrinsic value
Exercised, number of shares (in shares)	(460,725)
Exercised, weighted average exercise price (in dollars per share)	$ 0.50
Exercised, intrinsic value	$ 630,389
Expired or cancelled, number of shares (in shares)
Expired or cancelled, weighted average exercise price (in dollars per share)
Outstanding , number of shares (in shares)	613,446	3,249,171	1,074,171	1,500,000
Outstanding , weighted average exercise price (in dollars per share)	$ 0.50	$ 1.45	$ 0.50	$ 2.55
Exercisable, number of shares (in shares)	613,446	3,249,171
Exercisable, weighted average exercise price (in dollars per share)	$ 0.50	$ 1.45
Exercisable, weighted average remaining life (Year)	3 years 310 days	2 years 343 days
Exercisable, intrinsic value	$ 460,085