Refactor Process struct

[trizinix]

We can't prefetch all the properties for the user. We shouldn't be inconsistent if a property is prefetched or up-to-date. Hence we have to return always an up-to-date value.
The Process should be an opaque data type and we should provide the following methods to fetch the relevant property.

• process_pid
• process_ppid
• process_name
• process_exe
• process_cmdline
• process_create_time
• process_parent
• process_cwd
• process_username
• process_uids
• process_gids
• process_terminal
• process_nice
• process_ionice
• process_rlimit
• process_io_counters
• process_num_ctx_switches
• process_num_fds
• process_num_handles
• process_num_threads
• process_threads
• process_cpu_times
• process_cpu_percent
• process_cpu_affinity
• process_memory_info
• process_memory_info_ex
• process_memory_percent
• process_memory_maps
• process_children
• process_open_files
• process_connections
• process_is_running
• process_send_signal
• process_suspend
• process_resume
• process_terminate
• process_kill
• process_wait

[nibrahim]

Agreed. I made a mention of this in README.