Streamfs - ring buffer style file system for flash

This provides a simple file system that can be used with flash chips for logging or
writing large binary blobs that are not appropriate with the current setting-oriented
file system (e.g. for OTA updates)

It always writes in a circular manner through the flash, overwriting the oldest file or
eventually the beginning of the current file. When a new file is opened it is given a
file_id greater than the maximum previous one.

The direct API that is most useful is:
- PIOS_STREAMFS_OpenWrite - creates a file to write to
- PIOS_STREAMFS_OpenRead - opens a file to read from
- PIOS_STREAMFS_Close - closes the existing file
- PIOS_STREAMFS_Format - erase the whole filesystem

Then when a file is open you can use either
- PIOS_COM_SendBuffer
- PIOS_COM_ReceiveBuffer

To stream from the file systems.

This also includes unit test coverage of the file system which demonstrates writing and reading.

There is a logging module that demonstrates using this code to write logs when the flight controller is started. In addition, there is GCS code (loosely based on the picoC data transfer code) that will download the logs from the flight controller to a file. This has been tested on Sparky2 and I have viewed these logs with python.

fixed