Renaming .size() to .capacity() on ci::ConcurrentCircularBuffer<T>

[num3ric]

https://github.com/cinder/Cinder/blob/master/include/cinder/ConcurrentCircularBuffer.h#L110

To follow the standards, and because at least twice I've made the mistake of trying to using .size() instead of say .isNotFull(), assuming it was dynamic. (And yes I realize it's a stupid mistake to make given that doing a comparison would not be atomic.)

Thoughts?

[richardeakin]

Makes sense to me. Also, should probably be getCapacity(), to indicate that it isn't some typedef'ed standard container.

Does it work to change the size implementation to something like the following?:

size_t getSize() const
{
    std::lock_guard<std::mutex> lock( mMutex );
    return mNumUnread;
}

If we were to make these changes, now seems like a good time (break it good!).

[andrewfb]

Addressed in #852