Use go-pointer instead of uintptr hacks.

[mattn]

Fixes #791

[codecov-commenter]

Codecov Report

Merging #814 into master will increase coverage by 0.04%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##           master     #814      +/-   ##
==========================================
+ Coverage   46.44%   46.48%   +0.04%     
==========================================
  Files          12       12              
  Lines        1912     1908       -4     
==========================================
- Hits          888      887       -1     
+ Misses        888      885       -3     
  Partials      136      136              

Impacted Files	Coverage Δ
sqlite3.go	50.94% <70.00%> (ø)
callback.go	58.96% <85.00%> (+0.53%)	⬆️

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