atof \*- ascii to floating
converts a string to a floating
should point to a string containing the number;
the first unrecognized character ends the number.
The only numbers recognized are: an optional minus
sign followed by a string of digits optionally containing
one decimal point, then followed optionally by the
letter \fBe\fR followed by a signed integer.
There are none; overflow results in a very large
number and garbage characters terminate the scan.
routine should accept initial \fB+\fR, initial blanks, and \fBE\fR for \fBe\fR.
Overflow should be signalled.