New lang: Stoney Creek

This is the second iteration of language design.
it adds scopes variables.
Variables must be declared before use, but they
can be declared in both branches of an 'if', then
used afterwards as the one variable.

No hole-in-scope is allowed: names that are declared
cannot be redeclared in a subordinate scope.

A test program is included:
   make sayhello

Note that there are no useful error messages yet.
That is the next step.

Signed-off-by: NeilBrown <neil@brown.name>