docs: some manpage fixes

Some editorial changes so the man pages follow the standards.

References:
 procps#173

vmstat.8

@@ -1,6 +1,6 @@
 .\"  This page Copyright (C) 1994 Henry Ware <al172@yfn.ysu.edu>
 .\"  Distributed under the GPL, Copyleft 1994.
-.TH VMSTAT 8 "September 2011" "procps-ng" "System Administration"
+.TH VMSTAT 8 "2020-06-04" "procps-ng" "System Administration"
 .SH NAME
 vmstat \- Report virtual memory statistics
 .SH SYNOPSIS
@@ -98,19 +98,19 @@ b: The number of processes in uninterruptible sleep.
 .PP
 .SS
 .B "Memory"
-These are affected by the \-\-unit option.
+These are affected by the \fB\-\-unit\fR option.
 .nf
 swpd: the amount of virtual memory used.
 free: the amount of idle memory.
 buff: the amount of memory used as buffers.
 cache: the amount of memory used as cache.
-inact: the amount of inactive memory.  (\-a option)
-active: the amount of active memory.  (\-a option)
+inact: the amount of inactive memory.  (\fB\-a\fR option)
+active: the amount of active memory.  (\fB\-a\fR option)
 .fi
 .PP
 .SS
 .B "Swap"
-These are affected by the \-\-unit option.
+These are affected by the \fB\-\-unit\fR option.
 .nf
 si: Amount of memory swapped in from disk (/s).
 so: Amount of memory swapped to disk (/s).
@@ -184,7 +184,7 @@ size: Size of each object
 pages: Number of pages with at least one active object
 .fi
 .SH NOTES
-.B "vmstat "
+.B vmstat
 does not require special permissions.
 .PP
 These reports are intended to help identify system bottlenecks.  Linux