This function compress the given string using the DEFLATE data format.
For details on the DEFLATE compression algorithm see the document "DEFLATE Compressed Data Format Specification version 1.3" (RFC 1951).
The data to deflate.
The level of compression. Can be given as 0 for no compression up to 9 for maximum compression. If not given, the default compression level will be the default compression level of the zlib library.