Start of the 00.00.06 iteration.
call-sva instruction encoders and decoders
Behavior for call-sva and a sample program.
Version v00.00.06

This version adds support for procedures to call on primitives to
perform part of the work. For now it's slightly more limited than
the final goal on grounds of it primitives being only able to take a
single parameter and returning a single value.

Nonetheless, with carefully chosen primitives we can start
performing meaningful computations. For example, with primitives for
integer increment, integer decrement and integer predicate to detect
zeroes, we can write a simple program to perform the sum of an
integer to a non-negative integer.

Since we're only calling primitives, without any way to call other
procedures we still don't have any need to record a stack of calls,
because we'll always be executing either the main procedure of the
module or the code of some primitive.

After this version we add a single instruction to our machine:
call-sva, which stands for call-with-single-value-and-argument,
which for now is only capable of calling primitives.

The instruction call-sva takes three arguments: a local where to
store the result of the call, a local where to find the primitive
being called and a local storing the argument to be passed to the
primitive.