Introduced generic macros & means to call a real function

[hjagodzinski]

This PR introduces two generic macros CMOCK_MOCK_METHOD and CMOCK_MOCK_FUNCTION. The former wraps around MOCK_METHOD extending the CMockMocker class with a static member holding a pointer to a real function. This pointer can be accessed with the CMOCK_REAL_FUNCTION macro. Example:

#include <cmock/cmock.h>

#include "math.h"

class MathMocker : public CMockMocker<MathMocker>
{
public:
    CMOCK_MOCK_METHOD(int, add, (int, int));
    CMOCK_MOCK_METHOD(int, substract, (int, int));
};

CMOCK_MOCK_FUNCTION(MathMocker, int, add, (int, int));
CMOCK_MOCK_FUNCTION(MathMocker, int, substract, (int, int));

{
    MathMocker mock;

    EXPECT_CALL(mock, add(1, 1)).WillOnce(Return(11));
    ASSERT_EQ(11, add(1, 1)); // calling the mock

    EXPECT_CALL(mock, substract(1, 2)).WillOnce(Return(12));
    ASSERT_EQ(12, substract(1, 2)); // calling the mock

  ASSERT_EQ(2, CMOCK_REAL_FUNCTION(MathMocker, add)(1, 2)); // calling the real function
}

ASSERT_EQ(2, add(1, 1)); // calling the real function
ASSERT_EQ(-1, substract(1, 2)); // calling the real function

Resolves #17.