This function returns a compressed version of the input
data using the DEFLATE data
format, or FALSE if an error
is encountered. The optional parameter
level can be given as 0 for no compression up to
9 for maximum compression.
For details on the DEFLATE compression algorithm see the
document "DEFLATE Compressed Data Format Specification
version 1.3" (RFC 1951).
See also gzinflate(),
gzcompress(), gzuncompress(),
gzencode().