Further streamlining changes

[peterwilsoncc]

This is for merging into the branch 187-streamlining.

• f2dc120 - reduces regular expressions in tevkori_filter_content_images, replacing preg_replace_callback with str_replace
• 69ad5dd - warm cache properly (see Warm cache with proper functions #197), doesn't reduce DB calls from WP_Query.

[peterwilsoncc]

Added cbf7dcb
Wraps a filter around the regular expression pattern for gh-190, I named it tevkori_search_images_pattern but I am certain there is something better.

[joemcgill]

Interestingly, it looks like update_postmeta_cache() doens't give us the same benefit that we were getting before, which makes me think that we're benefiting from the whole post object being cached.

There seems to be some performance boost by removing the second preg_match call in f2dc120, but it seems very slight in the examples I've tested.

[peterwilsoncc]

I'll check out the other cache priming functions, maybe _prime_post_caches( $ids, false, true );

[joemcgill]

Related: #187

[joemcgill]

Thanks @peterwilsoncc. I've merged most of these changes in #200. Let's do cbf7dcb in a separate pull request. I want to make sure we've let the placement of this filter simmer for a bit so we don't end up introducing back-compat issues.