Compare R5RS functions with R7RS

There is a need to update some functions.

e.g.:

In R5RS function:

```scheme
(string-copy string)
```

was replaced with:

```scheme
(string-copy string)
(string-copy string start)
(string-copy string start end)
```

in [R7RS spec](https://standards.scheme.org/unofficial/errata-corrected-r7rs.pdf).

Another example are string and char comparators #298
and log function #301

Start by comparing the interpreter's implemented functions with the R7RS specification, using the string-copy example as an entry point. Review related issues #298 and #301 to identify the broader set of discrepancies; done means the relevant R5RS functions support the required R7RS behavior.

Written by the indexing model from the issue text.