Add support for the array querying function in a constant context

This patchs adds support for the $dimensions() and $unpacked_dimensions()
array functions. Since the argument is only used to get the type information
these functions can always be evaluated at compile time.

For the following functions if the dimension argument is constant or omitted
and the first argument is not dynamic (a string or dynamic array) they will
return the specified information.

  $left(), $right(), $high(), $low(), $increment() and $size()

Dynamic information and a variable second argument will be implement in a
future patch.
Merge branch 'master' of git://github.com/steveicarus/iverilog