#43 Use GIO for compressed file read / write

[Andrew Hardie]

Now that we have Glib, we should remove the dependency on external "gzip" to read/write compressed files and use GIO instead. The combination of GZlibCompressor and GConverterOutputstream should do exactly what we need, and then the only external dependency we can't easily get rid of is "less"/"more").

This is especially needful on Win32 where gzip may not be available.

[Stephanie Evert]

An advantage of the current approach is that the compression runs in parallel as a separate process, so integrating it via GIO would make some operations substantially slower.

Alternative solution for windows: provide gzip binary as part of the binary distribution and set up default paths in CQP to use this (e.g. expecting it to be in the same directory as the CQP binary).