Update with emscripten 1.7.8 (with asm.js)

* speex api calls to be prefixed with _
* changed buffers allocation to be ALLOC_NORMAL
instead of ALLOC_STATIC as it brings assertion
errors with latest emscripten.
* faster with asm.js
Cleanup, and update dist file.

* Cleanup Makefile.
* Minification giving errors with 2 errors
with closure_compiler in the emscripten generated code.
* Added two quirks in `src/types.js` when using
libspeex.js with -O3.
Implement encode/decode times using UserTiming API
NR_MEASURES_PER_SEC is the nr of frames encoded

* 40 frames is around 8000 samples
which means 1 second.
Added User Timing API polyfill.