Add support for tolerance when using lookup-matches

[Seddryck]

It should be possible to define a tolerance when defining a lookup-matches. Same tolerances than for equal-to should be supported.

The following-code is expected:

<lookup-matches>
   <join>
      <mapping candidate="DepartmentID" reference="Id" type="numeric"/>
   </join>
   <inclusion>
      <mapping 
         candidate="DepartmentName" 
         reference="LowerName" type="text" 
         tolerance="ignore-case"
      />
   </inclusion>
   <result-set>
      <query>
         select [DepartmentID] as Id, 
         Lower([Name]) as LowerName 
         from [HumanResources].[Department]
      </query>
   </result-set>
</lookup-matches>

[Seddryck]

Beta available at https://ci.appveyor.com/project/Seddryck/nbi/builds/23952102/artifacts in 1.21.0-beta.4