SizeFS
===========

A mock Filesystem that exists in memory only. Returns files of a size as
specified by the filename

For example, reading a file named 128Mb+1 will return a file of 128 Megabytes
plus 1 byte, reading a file named 128Mb-1 will return a file of 128 Megabytes
minus 1 byte

::

 sfs = SizeFS()
 print len(sfs.open('1B').read())
 1
 print len(sfs.open('2B').read())
 2
 print len(sfs.open('1KB').read())
 1024
 print len(sfs.open('128KB').read())
 131072


The folder structure can also be used to determine the content of the files::

 print sfs.open('zeros/5B').read(5)
 00000

 print sfs.open('ones/128KB').read(5)
 11111


File content can also be random::

 print len(sfs.open('random/128KB').read())
 131072
 print len(sfs.open('random/128KB-1').read())
 131071
 print len(sfs.open('random/128KB+1').read())
 131073


File content can be generated by restricted regex pattern by adding a directory::

 sfs.add_regex_dir("regex1","a(bcd)*e{4}[a-z,0,3]*")
 print len(sfs.open('regex1/128KB').read())
 131072
 print len(sfs.open('regex1/128KB-1').read())
 131071
 print len(sfs.open('regex1/128KB+1').read())
 131073