Remove most non-core predicates from hlds_goal.m.

compiler/hlds_goal.m:
    As above.

    Put some of the remaining stuff in a more logical order.

compiler/make_goal.m:
    This new module contains the predicates, previously in hlds_goal.m,
    that construct new goals.

compiler/hlds.m:
compiler/notes/compiler_design.html:
    Include the new module.

compiler/goal_form.m:
    Move to this existing module the predicates previously in hlds_goal.m
    that test whether goals have particular forms (which is the task of
    this module).

compiler/*.m:
    Conform to the above. Note that no module requires a new import
    of BOTH make_goal and goal_form.