unqualified `ptrdiff_t` & `size_t` use

[MattPD]

Is this intentional?

As of GCC 4.9 this is no longer supported (and it was never std. compliant) -- see "Header changes": https://gcc.gnu.org/gcc-4.9/porting_to.html // Edit: this appears to refer to the header inclusion missing entirely.

Currently #include <cstddef> is used in two places:

• https://github.com/Reactive-Extensions/RxCpp/blob/dbf9f5254d9284b7175c176b4112bf5e9cc5109f/Rx/v2/src/rxcpp/rx-includes.hpp#L103
• https://github.com/Reactive-Extensions/RxCpp/blob/dbf9f5254d9284b7175c176b4112bf5e9cc5109f/Ix/CPP/src/cpplinq/linq.hpp#L147

A fix would be to either:

• fully qualify each use of std::ptrdiff_t and std::size_t (there aren't that many)
• replace #include <cstddef> with #include <stddef.h>

I presume the choice may very well be a matter of preference :-)

[kirkshoop]

I would prefer explicit use of std::

I think there was variation across compilers and std libraries that caused the explicit std:: to fail. Any solution would need to pass travisci and appveyor :)

[MattPD]

OK, let's see if this passes! :-)

Edit: All checks have passed :-)

[kirkshoop]

Looks great!