library: <vmstat> api, updated for current linux state

library: <vmstat> api, updated for current linux state

Since last visited, there have been several new fields
added to the /proc/vmstat file. Now, we are caught up.

[ references shown below represent linux git commits ]

Reference(s):
. 6/2020, added 'pgscan_...' & 'pgsteal_...'
commit 497a6c1b09902b22ceccc0f25ba4dd623e1ddb7d
. 4/2020, added 'nr_shadow_call_stack'
commit 628d06a48f57c36abdc2a024930212e654a501b7
. 4/2020, added 'thp_...fallback_charge'
commit 85b9f46e8ea451633ccd60a7d8cacbfff9f34047
. 4/2020, added 'thp_file_fallback'
commit dcdf11ee144133328664d90836e712d840d047d9
. 4/2020, added 'nr_foll_pin_...'
commit 1970dc6f5226416957ad0cc70ab47386ed3195a6
. 9/2019, added 'nr_file_...'
commit 60fbf0ab5da1c360e02b7f7d882bf1c0d8f7e32a

Signed-off-by: Jim Warner <james.warner@comcast.net>