1.29.0 Release

• Numeric literals now support scientific notation. Unsuffixed exponent
  literals are exact decimal values (1e3, 1.5e-3, 2E8); add f for
  IEEE 754 floats (1e308f).
• Enums can now be backed by scalar string or int values:
  enum Status: string { Active = "active"; }. Backed variants expose a
  read-only .value, EnumName.from(value) returns the matching variant or
  throws, and EnumName.tryFrom(value) returns the variant or null.
  Backing values must be unique literals, and variants cannot mix backing
  values with associated data.