JobShopProblem is now a Mapping, not a list

- implementing all interface functions for JobShopProblem to behave like
a Mapping (e.g. dict) with (int, int) keys
this implements and closes #14

src/Parser/js1_style.py

@@ -45,7 +45,7 @@ class JobShop1Visitor(JobShopVisitor):
         return None
 
 
-def parse_string(inputdata: str) -> JobShopProblem:
+def parse_string(inputdata: str) -> List[JobShopProblem]:
     """parse string with jobshop1-formatted data (multiple problem instances)
     and return list of JobShopProblem s"""
     parse_tree = parser.parse(inputdata)