Replace single-precision with actual numerical precision

[rillig]

• I have searched open and closed issues and pull requests for duplicates, using these search terms:
  • precision
• I have checked the latest main branch to see if this has already been fixed, in this file:
  • src/ch03-02-data-types.md

Description of the problem:
The text says:

The f32 type is a single-precision float, and f64 has double precision.

These terms are from IEEE 754-1985 and have been superceded by IEEE 754-2008, which has renamed the types single and double to the more expressive binary32 and binary64.

Suggested fix:

• Reword the above quote to make it clear why this sentence is useful to a reader.
• Or reword the sentence stating the actual precision in decimal places, something like:
  • f32 has about 7 decimal places of precision, f64 has about 15 decimal places of precision.
• Or, even better, remove the sentence, as it is largely redundant.

[chriskrycho]

Indeed—and the 2008 revision by the 2019 revision! Which continues the use of the binary32 etc. naming. I think it’s probably helpful to indicate that it follows the standard but may not need the extra detail—I don’t imagine anyone would have any trouble inferring that f32 maps to binary32 etc.