More stable reading of FASTQ,FASTA,plain

1) Split code to read FASTQ/FASTA/plain files into three functions
- input files can't combine formats anymore
- cleaner code

2) Pulled latest version of stream_buffer.h from:
   [https://github.com/noporpoise/string_buffer]

3) Fixed memory leak: sf->path was not being free'd

4) Fixed bug where facat/fqcat weren't accepting -w 0 argument (no wrapping)

5) Added identification of .fsa as FASTA format extension