Lower RES Memory usage!

I got a new Microsoft Surface,  and the memory usage on RES is too much for the poor tablet.  So,  I decided to fork RES and see if I can reduce memory overhead for loading new pages.   If this patch goes well,  I'd like to further reduce RES's memory usage. 

This patch could use more testing.  Loading 10 pages with the current RES takes roughly 804M or ram,  after this patch the page consumed 764M with the same dataset.  Still needs more work,  but there is a noticeable reduction in memory usage with normal browsing habits.

Improvements:
- A bloomfilter is the most efficient way of keeping track of dupes.  A bloomfilter doesn't need to store the full string in order to keep track of uniqueness.  Additionally,  insertion into a bloom filter is always O(1), where as dictionaries need to be expanded when they become full.

-  "Hiding" elements with CSS doesn't make them go away.  These elements need to be deleted properly to free up memory. Hiding elements lead to a **nasty** memory leak.  Reddit has enough re-posts,  there is no need for RES to introduce duplicates to the feed.

I haven't looked into this and I'm on the go at the moment, but the real question is just how much memory savings we have here and whether or not the benefit outweighs the risk (which there is a slight one of false positives with a bloom filter) as well as the overhead - hashing isn't the most inexpensive thing int he world, so it's memory at the cost of CPU, right?

I have had no time or significant thought into just how much of one or the other we're using, but it's something we need to consider.

Regardless, I absolutely 110% appreciate the time and thought you've put into this and the suggestion of a way to potentially make RES more efficient - this is great.  I've been familiar with bloom filters, but it never really occurred to me to use one in RES so the suggestion is certainly welcome!