Rename global constant to match spec

[jtraglia]

• Rename variables to better match the spec.
  • I think ZeroPoint is a valid name, but just going with the spec here.
  • Also, the linters complained about these being ALL_UPPERCASE.
• Update comments a bit.
• Change from array of decimal integers to hexadecimal.
  • Also, wrap (4 lines of 8 bytes).
• Update tests to be a little cleaner.