vhdlpp: Elaborate all types of initializing expressions.
vhdlpp: Added VTypeEnum::write_to_stream().
vhdlpp: Added ExpBitString::write_to_stream().
vhdlpp: Added ExpString::write_to_stream().
vhdlpp: Fixed ExpAggregate::write_to_stream().
vhdlpp: Do not emit constants from packages.

They are elaborated and emitted by architectures that make use of packages.
vhdlpp: Skip writing '=>' for ExpAggregates if there are no fields specified.
vhdlpp: VTypeArray::range_t handles direction (to/downto).
vhdlpp: Inlined a few functions.
vhdlpp: Typedefs in packages are emitted before constants.
vhdlpp: Added VTypeArray::basic_type() to cope with
arrays based on typedefs.
vhdlpp: Corrected VTypeArray::write_to_stream().

Now it outputs "typedef(range)" instead of "array (range) of type".
Merge pull request #42 from orsonmmz/const_package

Enable constant initializers that require elaboration in packages.