Support "scoring" of a result-set

[Seddryck]

It should be possible to score a result-set. An assertion validates something and express how many rows don't go through the validation process. At the opposite the scoring is giving a unique value (a percentage), if this percentage is lower than the threshold then the test should fail.

The MVP:

<system-under-test>
  <scalar>
     <query>
         select 0.25
     </query>
  <scalar>
</system-under-test>
<assert>
   <score threshold="0.95"/>
</assert>

[Seddryck]

Beta available at https://ci.appveyor.com/project/Seddryck/nbi/build/1.19.0-beta.70.build.461/artifacts