helpers/string_validator library

1. eliud_core_helpers package
2. documentation
3. helpers/string_validator.dart

eliud_core_helpers package

1. Libraries
2. base/entity_base
3. base/model_base
4. etc/enums
5. etc/merge
6. etc/random
7. etc/screen_size
8. firestore/firestore_tools
9. helpers/common_tools
10. helpers/medium_collect_references
11. helpers/parse_helper
12. helpers/string_validator
13. query/query_tools
14. repository/repository_base
15. tools/delete_snackbar
16. tools/has_fab