While all the BIO_TYPE_* constants are part of the API, most of their

While all the BIO_TYPE_* constants are part of the API, most of their
values are only part of the ABI and not of the API, so delete them
from the SYNOPSIS: application programmers must not rely on the
specific values.

Instead of listing the specific values, properly describe the meaning
of all these constants.

However, the values of BIO_TYPE_NONE and BIO_TYPE_START are hard-coded
into the API and application programmers need to be aware of their
values, so those remain in the SYNOPSIS.