Note 13 - Employee Equity Incentive Plans - Stock Option Activity (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015	Dec. 31, 2014
Number of shares (in shares)	2,002,500	3,130,000
Weighted average exercise price (per share) (in dollars per share)	$ 0.14	$ 0.20
Weighted average remaining contractual term (in years)	1 year 361 days	1 year 146 days	1 year 215 days
Aggregate intrinsic value	$ 57,088	$ 198,990	$ 364,900
Number of shares, granted (in shares)	0	225,000
Weighted average exercise price (per share), granted (in dollars per share)	$ 0	$ 0.25
Number of shares, exercised (in shares)	(1,012,500)	(292,500)
Weighted average exercise price (per share), exercised (in dollars per share)	$ 0.13	$ 0.12
Number of shares, forfeited/cancelled/expired (in shares)	(7,500)	(1,060,000)
Weighted average exercise price (per share), forfeited/cancelled/expired (in dollars per share)	$ 0.13	$ 0.35
Number of shares (in shares)	982,500	2,002,500	3,130,000
Weighted average exercise price (per share) (in dollars per share)	$ 0.16	$ 0.14	$ 0.20
Vested and exercisable at June 30, 2016 (in shares)	845,000
Vested and exercisable at June 30, 2016 (in dollars per share)	$ 0.15
Vested and exercisable at June 30, 2016	1 year 255 days
Vested and exercisable at June 30, 2016	$ 54,938