Adding char const* buffer() const noexcept; method cpp

[kdoherty2]

In order to be able to pass a const reference of the SBE Message and access the underlying buffer
consider adding method:

char const* buffer() const SBE_NOEXCEPT;

char const* buffer() const SBE_NOEXCEPT
{
    return m_buffer;
} 

The generator only generates a non-const version:

char* buffer() SBE_NOEXCEPT
{
     return m_buffer;
}

[mjpt777]

I got tripped by the styling.