clarify usleep license

[bradrydzewski]

This pull request helps clarify the license of the usleep function. This usleep function originates from the PHP codebase and is therefore published under an OSI-approved license. However, linking to stackoverflow without linking back to the original source caused some problems during a recent license audit:

Anything from stackoverflow is under the Creative Commons Attribution ShareAlike 4.0 license which requires that any code that remixes, transforms or builds upon the material on stackoverflow be distributed under the same license. So Go-sqllite3 could potentially be violating stackoverflow TOS.

This change should clarify that this file is open source and does not violate the stackoverflow TOS, and should help avoid any license compliance challenges in the future 🙂

[codecov-io]

Codecov Report

Merging #893 (3f977d3) into master (223d277) will decrease coverage by 0.13%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #893      +/-   ##
==========================================
- Coverage   46.92%   46.78%   -0.14%     
==========================================
  Files          11       11              
  Lines        1447     1447              
==========================================
- Hits          679      677       -2     
- Misses        635      636       +1     
- Partials      133      134       +1     

Impacted Files	Coverage Δ
sqlite3.go	53.16% <0.00%> (-0.23%)	⬇️

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[mattn]

Thank you.