Various optimisations

[ThomasSevestre]

I've pushed some optimisations in my eventmachine branch.
They are not eventmachine related, it could be porter here.

The biggest optimisation is very simple :
ThomasSevestre@3aa907e

I also pushed an optimised lexer (50% improvement) :
ThomasSevestre@ad24ff8

[benlangfeld]

The logging one would need to be conditional. I'd accept a PR for it.

The optimised lexer is probably fine assuming it passes the tests but I don't have time to fully review it. Maybe @lpradovera could.

[ThomasSevestre]

I'm using my EM branch everywhere now and I won't be able to provide battle field tested PRs. My branch is based on an old version of the library, there might be small differences.

The optimised lexer passes the tests except for one little change . The test suite is very good by the way.

I've been using my branch in production without issue for over 9 months now. Feel free to cherry-pick what you want. The commit I pointed in my previous message had significant impact on CPU usage, even in an heavy application with a lot of ActiveRecord queries.