Update performance numbers in README

[noteflakes]

The sqlite3 gem version 2.0 is significantly faster than before. The benchmark results in the README should be updated to reflect that.

[joshuapinter]

@noteflakes This was a good shout. I came looking at extralite mostly because the memory consumption of a big import via sqlite3 was massive for us. 32 GBs or something and we were only moving towards bigger and bigger imports we were doing.

Seeing this comment you wrote made me check which version of sqlite3 we were using. We were on 1.7.3 so after upgrading to 2.0.2 that memory consumption nearly disappeared on the same import. I noticed an entry in the CHANGELOG saying something about a memory leak that they fixed.

So, in addition to the speed performance, it looks like the memory consumption has been greatly improved in sqlite3 version 2 as well.

When we have more time, I'd still like to check out extralite to see what kind of performance gains we get but also just a nicer interface to work with, it seems. Very well thought out and documented.

Thanks for making this comment here.