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These terms are from IEEE 754-1985 and have been superceded by IEEE 754-2008, which has renamed the types single and double to the more expressive binary32 and binary64.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