new directories layout, crossover instead of cljx, dependencies updates

Hello Creighton,
while learning your very interesting lib, I updated the deps and the plugins section. I even tried to restructure a little bit its directories layout.

* I updated the references to  the `cljsbuild` plugin to `"0.3.3"` which, in turn,  requires to update clojure to `"1.5.1"` release and to explicitly choose a CLJS release. I set the latest available (i.e. `"0.0-1909"`). the new `cljsbuild` release also require a min `"2.1.3"` lein version;
* I removed the `cljx` plugin, because when you have to deal with `portable clojure` code, I think the `:crossovers` option is much more comfortable (i.e. it requires much less configurations);
* I created the `src/clj` and `src/cljs` dirs under which I put the corresponding `enfocus` stuff
* I moved the `macros.clj` file under the `src/clj/enfocus/` dir
* I moved the previous syntax.cljx file under the `src/clj/enfocus/enlive` dir as `syntax.clj` (because of the switch from `cljx` to the `:crossovers` option of `cljsbuild`

IMHO there are still things that could be improved regrading the project codebase organization, e.g.
* separation on concerns between source code and testing code (you have the testing.cljs code in the source dir and even the html directory)
* introduction of the `clojurescript.test` lib by Chas Emerick for unit testing
* inclusion of the ring stuff inside the dev profile hosted in the `project/project.clj` file.  

But before eventually collaborate on that points, I'd like to know from you what do you thing about the proposed pull request.

My best