Update simd.js for upstream changes.

The main change relevant to Emscripten here is that this includes the
fix for unaligned loads and stores.
[tracing] Add task tracing.
[tracing] Context data is used on the server side now.
[tracing] Add a way to track "associated storage size".

The docs cover this in more detail.
[embind docs] Reformat and cleanup whitespace.
Rename simd.jd to ecmascript_simd.js

Since that's what the upstream name of this file is. Note that we are
still using a branch of upstream rather than plain upstream.
1.26.0
Implement _mm_loadu_ps and _mm_storeu_ps
Merge pull request #2929 from waywardmonkeys/embind-docs

[embind docs] Reformat and cleanup whitespace.
Merge pull request #2928 from waywardmonkeys/trace-extensions

Trace extensions
use system libs args processing in precompiled headers
option to use zlib from ports