Added RAM access functions, removed overloaded begin() function

[kgmossey]

Bug fix: The Wire.h in the ESP32 library has the ability to set the SDA and SCL pins, but the Arduino Wire.h does not. Anyone trying to use this on an Arduino will get the "no matching function for call to 'TwoWire::begin..." as mentioned in the one issue on this library. I've removed that function so that it will compile properly on Arduino/AVR chips as well as ESP32. When the Arduino library is updated we can replace this function (which is super cool).

Feature add: I've added functions to read and write to RAM. The functions are fairly intuitive, I think.

void getRam() reads the contents of the DS1307 chip into a variable called "ram" which is publicly accessible.
void setRam() writes the contents of "ram" to the DS1307 chip.

If you only need to read/write an address, you can individually set each address to a specific 8 bit value (this saves time over reading/writing the entire ram buffer):

void setRamAddress(uint8_t _addr, uint8_t _value) sets a specific address (_addr) to a value (_value). It also updates the ram buffer.
uint8_t getRamAddress(uint8_t _addr) returns the value at a specific address (_addr)

RAM addresses are 0 indexed.

[kgmossey]

Added doxygen style function descriptors and a conditional compilation to keep the changes by Saffarofski in the code, but they won't compile since Arduino_h will always be defined. This way for those that want to use them they can just by removing the conditional compilation declarations, but the compile won't fail on Arduino builds.

[isidromv]

Thanks for fixing the bug with begin(), I have left a minor comment on your implementation of RAM management.

[isidromv]

This blocks 56 bytes of precious memory, even if the user doesn't plan to manipulate the RAM directly. What about setRam and getRam accepting this as a parameter instead of an internal variable? In this way, only the users requiring it need to allocate the 56 bytes beforehand.