Note 6 - Warrants - Warrants Outstanding (Details) - USD ($)		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Balance, outstanding (in shares)		26,872,430	22,104,817
Balance, outstanding, price range (in dollars per share)
Granted (in shares)		24,490,687	7,451,013
Granted, price range (in dollars per share)
Expired (in shares)		(587,500)	(2,683,400)
Expired, price range (in dollars per share)		$ 0.40	$ 0.40
Exercised (in shares)		(7,544,456)
Exercised, price range (in dollars per share)		$ 0.30
Balance, outstanding (in shares)		43,231,161	26,872,430
Balance, aggregate intrinsic value	[1]
Minimum [Member]
Balance, outstanding, price range (in dollars per share)		$ 0.25	$ 0.25	0.25
Granted, price range (in dollars per share)		0.25	0.25
Expired, price range (in dollars per share)
Exercised, price range (in dollars per share)
Maximum [Member]
Balance, outstanding, price range (in dollars per share)		1	1	1
Granted, price range (in dollars per share)		0.48	0.48
Expired, price range (in dollars per share)
Exercised, price range (in dollars per share)
Weighted Average [Member]
Balance, outstanding, price range (in dollars per share)		0.43	0.43	$ 0.45
Granted, price range (in dollars per share)		0.29	0.29
Expired, price range (in dollars per share)		0.40	$ 0.40
Exercised, price range (in dollars per share)		$ 0.30

[1] Aggregate intrinsic value based on closing common stock price of $0.22 at December 31, 2019.