Style: data_types

[umarcor]

This PR is based on VUnit#481 and it should be merged later.

This PR is work-in-progress towards VUnit#476 and VUnit#470.

• The style of functions and procedures in almost all the sources in vunit/vhdl/data_types/src is modified:

function
func_name(
  paramA : typeofparamA
) return typeofreturn;

• end function; and end procedure; are replaced with end; for coherency.

• Aliases are added to integer_vector_ptr and string_ptr in order to highlight the similarities between these files. Compare, e.g., integer_vector_ptr_pkg-body-200x.vhd and string_ptr_pkg-body-200x.vhd before and after this PR:

Added(4,28)  Deleted(0,19) Changed(88) Changed in changed(71)
Added(40,16) Deleted(0,25) Changed(63) Changed in changed(43)

• The definition of types integer_vector_t, integer_vector_access_t, string_ptr_access_t, etc. are moved to separate packages in a new subdir (vunit/vhdl/data_types/src/types). This is because, in the future, packages to support external models will depend on these types, and integer_vector_ptr_pkg/string_ptr_pkg will depend on the external models (or their placeholders).

• In the VHDL 2008 sources, there is no need to use custom types for the pointers. 'natural' is used instead.

• When external models are added, the variable inside the pointer types will not be an explicit index. I think that ref is a better name.

• GHDL drops a lot of warnings because declaring parameter length hides the function name. Options are renamed to len to avoid it.

• Parameter index used in get and set is declared as of type integer. However, it should be natural, because it is not possible to access to negative indexes.