cleaner representation of index

Cargo.lock

@@ -234,6 +234,12 @@ dependencies = [
  "winapi 0.3.9",
 ]
 
+[[package]]
+name = "fixedbitset"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0ce7134b9999ecaf8bcd65542e436736ef32ddca1b3e06094cb6ec5755203b80"
+
 [[package]]
 name = "fnv"
 version = "1.0.7"
@@ -496,6 +502,18 @@ version = "2.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d4fd5641d01c8f18a23da7b6fe29298ff4b55afcccdf78973b24cf3175fee32e"
 
+[[package]]
+name = "petgraph"
+version = "0.6.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e6d5014253a1331579ce62aa67443b4a658c5e7dd03d4bc6d302b94474888143"
+dependencies = [
+ "fixedbitset",
+ "indexmap",
+ "serde",
+ "serde_derive",
+]
+
 [[package]]
 name = "proc-macro-error"
 version = "1.0.4"
@@ -832,6 +850,7 @@ dependencies = [
  "colored",
  "comfy-table",
  "confy",
+ "petgraph",
  "serde",
  "serde_with",
  "termsize",