ENH: add expression support for scalar/vector expression lookups

- similar idea to swak timelines/lookuptables but combined together
  and based on Function1 for more flexibility.

  Specified as 'functions<scalar>' or 'functions<vector>'.
  For example,

  functions<scalar>
  {
      intakeType table ((0 0) (10 1.2));

      p_inlet
      {
          type        sine;
          frequency   3000;
          scale       50;
          level       101325;
      }
  }

  These can be referenced in the expressions as a nullary function or a
  unary function.

  Within the parser, the names are prefixed with "fn:" (function).
  It is thus possible to define "fn:sin()" that is different than
  the builtin "sin()" function.

     * A nullary call uses time value
       - Eg, fn:p_inlet()

     * A unary call acts as a remapper function.
       - Eg, fn:intakeType(6.25)