Blast it X:( Gave up after going >80% of the way

I correctly identified the transform f(i) |--> Ni/(Di + f(i + 1)), to be
performed till the limit k is reached. Also identified a  need for a
loop inside cont-frac.

Yet I went stupidly alllll over the place, for a whole day, trying to
implement it with let and/or lambda and gave up, and looked at the
answer at Scheme-wiki.

The direct answer is so trivial. I should have persisted.  Yeesh :(

Hat tip Scheme-wiki.
Fixed if-condition in count-frac-iter

Testing for count '<=' 2 was plain wrong... it should be just count '='
1. This is because the loop is invoked with an already-decremented
value. To be specific, if the current value of (count - 1) in the loop
is 2, then it must compute d (2 - 1) +  n(2)/result. i.e. the
if-condition must allow the result to be transformed as long as count is
2 or more, and should terminate only when the countdown value reaches 1.

This bug was revealed when I used the (buggy) cont-frac-iter procedure
to compute Euler's constant e, as asked in ex.1.38.
Compute Euler's constant

This definition allows me to control which continued fraction procedure
I use, to compute the constant. I did this to test how fast the
computations converge for the recursive and the iterative processes.
Iterative and recursive variants. It's working!

Compare computation with Scheme's built-in 'tan' primitive.