minor doc changes in prep for merge
Merge pull request #50 from kitwestneat/master

allow wp-config.php specified varnish_servers to define secret.
add @ to suppress Undefined Offset notice
fix docs
Merge pull request #51 from cd34/master

fix for issue #50, doc fixes
fix typo: 'WPVarnishPurgePurgeCommonObjects'

'WPVarnishPurgePurgeCommonObjects' should be 'WPVarnishPurgeCommonObjects'