pgsql: Make a copy-editing pass over the new documentation for statisti

Make a copy-editing pass over the new documentation for statistics views.

Fix a bunch of typos, improve markup, make wording more uniform, rearrange
some material.  No substantive changes.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/aebe989477ac5a9f7b59ae464ec68ec45975ed3f

Modified Files
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doc/src/sgml/monitoring.sgml | 1282 +++++++++++++++++++++---------------------
1 files changed, 633 insertions(+), 649 deletions(-)