Fixes to building from source sections (incomplete)
Fixed wget2 tests by adding ST_ABORTED	 request status
Fixes to allow webidl_binder.py generated code to work with closure
Fix off-by-one error when writing JSImplementation virtual method calls.
Enable closure in asm2.test_webidl
Must access TypeTestClass via Module
Merge branch 'incoming' of https://github.com/hamishwillee/emscripten into incoming

Conflicts:
	site/source/docs/building_from_source/building_emscripten_from_source_on_windows.rst
	site/source/docs/building_from_source/installing_from_source.rst
export Module for node in test_webidl; #2620
Merge branch 'webidl-bugfixes' of https://github.com/artillery/emscripten into incoming
remove Module hack from webidl binder
convert socket callback declarations to use typedefs for function pointer types
add preamble.js.html build doc
build libcx and libcxxabi with -Oz, for size
stop testing sanity.test_nostdincxx on old i386 target
update sanity.test_emcc_caching
1.21.1
add fastcomp stack overflow checks and testing
explicitly provide Module to EM_ASM scripts, so that they work even if Module was removed by closure; #2639
Update emscripten.h, html5.h docs to match the source files
Remove comments from preamble.js. Add link to doc file and built version