ext function call are pushed via the
<code class="mendoza-code">PUSH</code>, <code class="mendoza-code">PUSH2</code>, <code class="mendoza-code">PUSH3</code>, and <code class="mendoza-code">PUSHA</code> instructions. The
stack of a fiber will grow as large as needed, although by default Janet will
limit the maximum size of a fiber's stack.  The maximum stack size can be
modified on a per-fiber basis.
</p>
<p>The slots in the stack are exposed as virtual registers to instructions. They
can hold any Janet val