Tracking issue for process::Process missing methods

[svartalf]

There is a lot to add to process::Process struct, this issue should help to track the missing things. Method names are based on psutil naming, so there might be some renaming made during the implementation process later.

• cmdline: process::Process::cmdline for Linux #97, process::Process::cmdline for macOS #98, process::Process::cmdline for Windows #99
• environ: process::Process::environment for Linux #208, process::Process::environment for macOS #209, process::Process::environment for Windows #210
• create_time: process::Process::create_time for Linux #100, process::Process::create_time for macOS #101, process::Process::create_time for Windows #102
• cwd: process::Process::cwd for Linux #103, process::Process::cwd for macOS #104, process::Process::cwd for Windows #105
• username: Process::user method #194
• uids
• gids
• terminal
• nice: Process::niceness for *nix systems #216, Process::priority for Windows #217
• ionice
• rlimit
• disk_io_counters: Process disk IO counters for Linux #127
• net_io_counters: process::Process::net_io_counters for Linux #124
• num_ctx_switches
• num_fds
• num_handles
• num_threads
• threads
• cpu_times: process::Process::cpu_times method for Linux #107, process::Process::cpu_times method for macOS #108, process::Process::cpu_times method for Windows #109
• cpu_percent: process::Process::cpu_percent for Linux #134, process::Process::cpu_percent for macOS #135, process::Process::cpu_percent for Windows #136
• cpu_affinity
• cpu_num
• memory_info: process::Process::memory for Linux #121, process::Process::memory for macOS #122, process::Process::memory for Windows #123
• memory_full_info
• memory_maps
• children
• open_files
• connections
• is_running: process::Process::is_running for Linux #151, process::Process::is_running for macOS #152, process::Process::is_running for Windows #153
• send_signal: process::Process::signal for nix systems #156
• suspend: process::Process::suspend and ::resume for nix systems #164, process::Process::suspend for Windows #165
• resume: process::Process::suspend and ::resume for nix systems #164, process::Process::resume for Windows #166
• terminate: process::Process::terminate for nix systems #162, process::Process::terminate for Windows #163
• kill: process::Process::kill for nix systems #158, process::Process::kill for Windows #159
• wait: Process::wait for Linux #213, Process::wait for macOS #214, Process::wait for Windows #215