Idea: Ship `upx`-compressed executables?

[k3rni]

Using upx on shipped wkhtmltopdf binaries drastically reduces their size. Each of the binaries (linux x86, linux x86_64, darwin x86) reduces to about 15MB. And with modern CPUs the decompression time doesn't matter - but there is less I/O involved.

[joevandyk]

@k3rni could you do this for each of the platforms and make a pull request?

[k3rni]

@joevandyk see #47