Support temporal assertions regarding the absence of overlap for a time tick

[Seddryck]

It should be possible to assert that a result-set, with a column for time tick has no overlap in the definition of this time-period. A time tick is defined as the closed-open time interval between a datetime and a timespan.

<system-under-test>
  <result-set>
    ...
  </result-set>
</system-under-test>
<assert>
  <without-overlaps>
    <time-tick start="#3" span="TimeSpanColumn"/>
    <group-by>...<group-by>
  </without-overlaps>
</assert>

The optional group-by let you define that system-under-test rows should not be tested as a single set of rows but should be subdivided into subsets, each subset being defined by the group-by.