Convert apps/bleuart/src/fifo to Mynewt library/module

[microbuilder]

The BLE UART helper currently uses the FIFO code from previous projects.

The code itself is well written and useful, but it would probably be better to stick to the buffers already available in Mynewt for statistic collection and debugging purposes, and just to improve our chances of getting future pull requests integrated into the core codebase.

Some of the buffer and queue options defined as part of Mynewt are:

• Memory Pools
• Memory Buffers (mbuf)
• mqueue <-- This seems to replace a FIFO

These should be evaluated to see if there isn't something that matches the FIFO/buffering needs for BLE UART and other services.

Some related buffer elements worth exploring in the future are:

• Flash Circular Buffer - A flash based FIFO of sorts

[microbuilder]

Alternatively, we can convert the FIFO.* code into a Mynewt library so that it can be maintained and reused, and improve our chances of having pull requests accepted.

[microbuilder]

Unfortunately, the minimum size for mempool is a word, so 4 bytes, which makes it very inefficient for UART style FIFOs that deal with one byte at a time. Adapting FIFO to be a library seems like the best approach.

[microbuilder]

This isn't documented, but might be a valid 'standard' alternative to the custom FIFO code: https://github.com/apache/incubator-mynewt-core/blob/master/libs/util/src/cbmem.c

[hathach]

cbmem is a variable-length FIFO, each time an item is pushed into the buffer, it will create an header (4 bytes) for each item. It still has an huge overhead considering the item size of bleuart is probably 1 or 2 most of the time.

[microbuilder]

Lets plan on creating a custom FIFO module later then, but leave this as is for now. I'll keep the issue open until the FIFO module is implemented though (in Mynewt library/module form).

[hathach]

OK, let's leave it as it is. I am trying to add both newtmgr (serial) & newtmgr over ble to our project.