Use setuptools and fallback to distutils
Add 'pythonz' entrypoint, useful for system-wide installations
Simplified setting PATH environment variable

It failed if any entries in $PATH had a '.', and I don't have the
patience to debug it. If you are concerned about duplicated entries add
this to your bashrc:

export PATH=$(echo "$PATH" | awk -v RS=':' -v ORS=":" '!a[$1]++{if (NR > 1) printf ORS; printf $a[$1]}')