Added support for PIC32 return types

[majenkotech]

This simply abstracts const __FlashStringHelper or const char into a macro CCRET (Const Char RETurn) chosen by the existence of the macro __PIC32__ so the library works properly with the chipKIT system.

[Rotzbua]

Hi, thanks. But wouldn't it be easier to just use

#ifdef __PIC32__
#define __FlashStringHelper char
#endif

?

[majenkotech]

I tried various combinations of that with another library and it completely barfed with overloads where you have a FlashString and a char variant of the same function. In this one specific situation where it's only returning a value it may work better.

[Rotzbua]

As I mentioned in #216 (comment) . I would like too keep this library as simple as possible. So board/platform specific changes should be done by the Arduino IDE plugin.

Would it be ok, if I mention your compatibility patch for the chipKIT in the readme? @majenkotech

[majenkotech]

Looking at the chipKIT implementation of __FlashStringHelper I am wondering if we actually have it right. We have const char *, which breaks things. Changing it to just plain char fixed your library but breaks overloading in others. One in particular has:

typedef const __FlashStringHelper *FlashString;

And then later has:

void dbg(FlashString str);
void dbg(const char *str);

And they of course crash with each other.

I am thinking switching to char for __FlashStringHelper is probably the best way to go.

[majenkotech]

I have been having a play with reinterpret_cast and such, and I think I have a more elegant solution. You can close this PR now I guess, it's not going to be needed any more.

[spudspud]

Where do i get codes for mfrc-522