Add find utility method for searching for issues among multiple issue states.

src/pitpkg/private/libpit.nim

@@ -385,6 +385,14 @@ proc filter*(issues: seq[Issue], filter: IssueFilter): seq[Issue] =
   for exclTag in filter.exclTags:
     result = result.filterIt(it.tags.find(exclTag) < 0)
 
+proc find*(
+    issues: TableRef[IssueState, seq[Issue]],
+    filter: IssueFilter
+  ): seq[Issue] =
+
+  result = @[]
+  for stateIssues in issues.values: result &= stateIssues.filter(filter)
+
 ### Configuration utilities
 proc loadConfig*(args: Table[string, Value] = initTable[string, Value]()): PitConfig =
   let pitrcLocations = @[