Merge pull request #169 from ebfe/comm

add comm
add cksum
Merge pull request #170 from ebfe/cksum

add cksum
Add unlink command.
Merge pull request #171 from zvms/add-unlink

Add unlink command.
Update for getopts changes
Update tests to use std::process:Command
Merge pull request #172 from ebfe/strbuf-getopts

Update for getopts changes
Merge pull request #173 from ebfe/fix-make-test

Update tests to use std::process:Command
Add cp back to Makefile and fix build.
Merge pull request #174 from ebfe/fix-cp

Add cp back to Makefile and fix build.
du: cope with path removal from FileStat
Merge pull request #175 from ebfe/fix-du

du: cope with path removal from FileStat
add tr
tr: add some tests
Merge pull request #177 from ebfe/tr

Add a basic tr
comm: add --version
comm: add --output-delimiter