[FixedCircularBuffer] Add FixedCircularBuffer

[abeimler]

Hi, I added a first FixedCircularBuffer implementation (#76) (you can use it as a draft and extend it). I added some features I use on my own.

• Use some parts of ETL circular_buffer https://www.etlcpp.com/circular_buffer.html
• Based on FixedQueue (uses FixedDeque)
• TODO: add in BUILD.bazel

_was not sure if or how to use CircularIntegerRangeIterator, so I used a plain size_t for the buffer cursor._
Had to make some methods public in FixedDeque

[alexkaratarakis]

Thanks! I also have been working on an implementation, but discovered a serious bug in FixedDeque. Going for the full FixedDeque API.

The is_full() vs available() differentiation came up as well (but I haven't addressed that yet). edit: Actually I misread available(). The consideration I had in mind was that while FixedCircularBuffer can be full because size() == MAXIMUM_SIZE, you can always still push to it anyway, which is different than all other fixed_containers. This means the following usual pattern doesn't quite fit FixedCircularBuffer

if (is_full(x))
{
    x.push_back(....);
}

May not be a problem, however.

Will push the current WIP in a few hours.

[alexkaratarakis]

Here is what I have so far: https://github.com/teslamotors/fixed-containers/pull/80 The second to last commit ("[FixedDeque] Rework deque state/iterators to fix iterator desync ") is the aforementioned serious bug. The last commit is adding the new container.

[alexkaratarakis]

Merged as part of #80 under the name FixedCircularQueue, to differentiate from FixedCircularDeque.