Start documenting qcache module, fix signature of QCache.__exit__, so it
does not override builtin type function.
Document and refactor QCache.run10 method. Make it more readable and
pass pylint checks.
Implement padding in QCache.run10 without a loop
Document and refactor QCache.run1 method. Improve readability, decrease
pylint violations. Add note about possible logical inconsistency in
caching of only first row in result of the query.
Move code testing qcache module to separate function, so it does not
pollute global scope. Make this code pass pylint checks.