Return ruby String from argv_of_pid instead of copying data
Use current process info in darwin test as otherwise cmdline can be nil
Get fields from ProcTableStruct
Add description to each field
Read saved pathname of the executed command to exe
Read environment variables to environ
Use sleep process for testing on darwin, add assertions and tests

Add equality assertions for pid, ppid, pgid, ruid, rgid, comm, cmdline
Add tests for exe and environ
Populate euid, egid, groups, svuid and svgid for darwin
Merge branch 'extend-darwin' into travis/extend-darwin