feat(boss): Boss creates nests and assigns registry crows (#43)

crowreg.go

@@ -86,6 +86,12 @@ func (s *CrowStore) Add(c SpunCrow) error {
 	return nil
 }
 
+// Has reports whether a crow with that name is in the registry.
+func (s *CrowStore) Has(name string) bool {
+	_, ok := s.Get(name)
+	return ok
+}
+
 // Len is how many crows the registry holds.
 func (s *CrowStore) Len() int {
 	s.mu.Lock()