perf_counter tools: Tidy up manpage details

Also fix a misalignment in usage string printing.

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

Documentation/perf_counter/Documentation/perf-help.txt

 perf-help(1)
-===========
+============
 
 NAME
 ----

Documentation/perf_counter/Documentation/perf-list.txt

 perf-list(1)
-==============
+============
 
 NAME
 ----
@@ -8,7 +8,7 @@ perf-list - List all symbolic event types
 SYNOPSIS
 --------
 [verse]
-'perf list
+'perf list'
 
 DESCRIPTION
 -----------

Documentation/perf_counter/Documentation/perf-stat.txt

 perf-stat(1)
-==========
+============
 
 NAME
 ----

Documentation/perf_counter/Documentation/perf-top.txt

 perf-top(1)
-==========
+===========
 
 NAME
 ----