Real type support for vhdlpp.

- Added support for real type in vhdlpp
The essential part, explained in the blueprint.

- Minor cleaning for valgrind output
This is optional. It just removes a few negligible entries from valgrind output log.

- Avoid freeing the primitve types classes
It is a fix for cases when there are two or more constants of the same primitive type declared. Upon the destruction of the second const_t object, it deletes the same VTypePrimitive for the second time, ending with segfault.

- Increase the output precision for floating point types.
One directive for std::cout to include more digits when it outputs floating type numbers. The unit test will not pass without that commit.