Add rewrites to vhost directories

[#MODULES-111](https://tickets.puppetlabs.com/browse/MODULES-111): Duplicate rewrites parameter from apache::vhost
as an array of hashes placed in the directories parameter
to enable use of mod_rewrite directives in vhost directories.

Add documentation to Parameter directories for apache::vhost for
rewrites array.

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This doesn't achieve the fully desired goal of  "support configuration via the other `templates/vhost/_*.erb` template fragments, ie `_rewrite.erb` and `_custom_fragment.erb` via the matching parameters for the fragment without code duplication."  from  MODULES-111    as it duplicated code.

However it achieves mod_rewrite functionality, and  custom_fragment  functionality in directories was added in a very similar manner.