Added checks to make sure the specified track exists

Added precondition checks to validate input files and paths to return more informative error messages as per #2

node_modules/json-schema/draft-04/links

@@ -0,0 +1,41 @@
+{
+	"$schema" : "http://json-schema.org/draft-04/hyper-schema#",
+	"id" : "http://json-schema.org/draft-04/links#",
+	"type" : "object",
+	
+	"properties" : {
+		"rel" : {
+			"type" : "string"
+		},
+
+		"href" : {
+			"type" : "string"
+		},
+
+		"template" : {
+			"type" : "string"
+		},
+		
+		"targetSchema" : {"$ref" : "http://json-schema.org/draft-04/hyper-schema#"},
+		
+		"method" : {
+			"type" : "string",
+			"default" : "GET"
+		},
+		
+		"enctype" : {
+			"type" : "string"
+		},
+		
+		"properties" : {
+			"type" : "object",
+			"additionalProperties" : {"$ref" : "http://json-schema.org/draft-04/hyper-schema#"}
+		}
+	},
+	
+	"required" : ["rel", "href"],
+	
+	"dependencies" : {
+		"enctype" : "method"
+	}
+}