The version does streaming using the 'streaming' library.
The library is, in general, in a "preview" state. In cases where you need to scan large FASTA files fast and with low memory overhead, the functions within should already be useable enough.
The wikipedia has information on the format:
http://en.wikipedia.org/wiki/FASTA_format
Christian Hoener zu Siederdissen
Leipzig University, Leipzig, Germany
[email protected]
http://www.bioinf.uni-leipzig.de/~choener/