Add support for passing integers to Context::setMode

[MauricioFauth]

I'm not confident about extracting the SQL mode constants from the Context class (#369), so I just improved the constants documentation blocks and I also added support for passing a combination of Context::SQL_MODE* constants to the Context::setMode method.

Closes #369

[codecov]

Codecov Report

Merging #370 (504f8fb) into master (9cf3396) will increase coverage by 0.15%.
The diff coverage is 94.87%.

@@             Coverage Diff              @@
##             master     #370      +/-   ##
============================================
+ Coverage     95.41%   95.57%   +0.15%     
- Complexity     2059     2094      +35     
============================================
  Files            67       67              
  Lines          4410     4478      +68     
============================================
+ Hits           4208     4280      +72     
+ Misses          202      198       -4     

Impacted Files	Coverage Δ
src/Tools/TestGenerator.php	0.00% <0.00%> (ø)
src/Utils/CLI.php	97.65% <0.00%> (ø)
src/Context.php	98.31% <100.00%> (+4.67%)	⬆️

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