Out parameter support

[krevels]

This provides support for the usage of sql.Out parameters with the sqlmock driver. While this partially addresses #144 , it should be noted that this isn't a matcher for sql.Out values, and users will likely have to use a custom matcher or AnyArg() for now.

[krevels]

I wanted to preserve the CheckNamedValue functionality for 1.8, but provide my own for 1.9+. I wasn't sure if there was a better way to handle doing that though 😅

[codecov-io]

Codecov Report

Merging #174 into master will decrease coverage by 0.6%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master     #174      +/-   ##
==========================================
- Coverage   91.25%   90.64%   -0.61%     
==========================================
  Files          13       15       +2     
  Lines         720      727       +7     
==========================================
+ Hits          657      659       +2     
- Misses         44       49       +5     
  Partials       19       19

Impacted Files	Coverage Δ
sqlmock_go18.go	100% <ø> (ø)	⬆️
sqlmock_go18_19.go	0% <0%> (ø)
sqlmock_go19.go	71.42% <71.42%> (ø)

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[l3pp4rd]

good change, thanks ;)