Builds the uutils multicall binary containing all utils (except stdbuf)
by default. To only build a subset
`cargo --no-default-features --features <utils>`
can be used.
Whats missing is building the standalone binaries and a mechanism to
automatically disable the build of unix only utils on windows.
There are several areas needing improvement:
1) add tests for hard links
2) add implementation for uncommon flags (-d, -L, -n, -P, -r)
3) align error messages more closely with GNU implementation
