Upgrade to `ion_rs` dependency to v1.0.0-rc.5

[zslayton]

• Upgrades the ion-cli's dependency on ion_rs from v1.0.0-rc.2 to v1.0.0-rc.5.
• Removes our dependency on memmap; all commands are now streaming.
• Removes hack to add newlines between per-file outputs from dump.
• Overhauls the inspect command to take advantage of new tooling access APIs in the streaming reader. The new version:
  • shows opcodes and VarUInt lengths in a style that is distinct from that of the body of the value
  • uses Unicode box drawing to render its table
  • colors annotations and field names in the text Ion column
  • shows the symbol ID assigned to each string in a local symbol

Fixes issues #34 and #36.

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