apache_vhosts: minor enhancement to readme
apache_vhosts: minor fix to options documentation
apache_vhosts: remove unused variables
apache_vhosts: avoid the use of eval
apache_vhosts: avoid data loss

The counters should be reset right after being read, while still holding
the write lock on the shared data, to avoid overwriting data the
collector process might have put in while we were busy generating the
graph.