Better error messages for table conflicts

[kylejlin]

Currently, debugging table conflicts is a horrible user experience, due to poor error messages, like this:

  (base) kyle@MacBookPro ave_v3 % cargo test
   Compiling ave_v3 v0.1.0 (/Users/kyle/zo/ave_v3)
error: failed to run custom build command for `ave_v3 v0.1.0 (/Users/kyle/zo/ave_v3)`

Caused by:
  process didn't exit successfully: `/Users/kyle/zo/target/debug/build/ave_v3-02ff28b9b95dcec2/build-script-build` (exit status: 101)
  --- stderr

  thread 'main' panicked at ave_v3/build.rs:38:21:
  Invalid Kiki file ./src/raw_parser.kiki. Error: TableConflict(
      TableConflictErr {
          state_index: StateIndex(
              151,
          ),
          items: (
              StateItem {
                  rule_index: Original(
                      50,
                  ),
                  lookahead: Terminal(
                      DollarlessTerminalName(
                          "Comma",
                      ),
                  ),
                  dot: 0,
              },
              StateItem {
                  rule_index: Original(
                      51,
                  ),
                  lookahead: Terminal(
                      DollarlessTerminalName(
                          "Comma",
                      ),
                  ),
                  dot: 0,
              },
          ),
          
          // ...lots of hard-to-understand information...
      },
  )

We should print out the conflicting rules (not just their indices).