Change the interface again, hopefully this time a bit more normal.
Now we wrap the emscripten module completely and just expose the
high level objects.

The olm library export is now imported as normal (ie. returns
a module rather than a function returning a module) but has an
`init` method which *must* be called. This returns a promise
which resolves when the module is ready. It also rejects if the
module failed to set up, unlike before (and unlike the
promise-not-a-promise that emscripten returns).

Generally catch failures to init the module.

Quite a lot going on in this PR:
 * Updates to support recent emscripten, switching to WASM which is now the default
 * Use emscripten's MODULARIZE option rather than wrapping it ourself, since doing
   so in pre-post js doesn't work anymore.
 * Most changes are moving the emscripten runtime functions to top-level
   calls rather than in the Module object.
 * Get rid of duplicated NULL_BYTE_PADDING_LENGTH
 * Fix ciphertext_length used without being declared
 * Fix things that caused the closure compiler to error, eg. using
   OLM_OPTIONS without a declaration.
 * Wait until module is inited to do OLM_ERROR = olm_error()

The main BREAKING CHANGE here is that the module now needs to initialise
asyncronously (because it has to load the wasm file). require()ing olm
now gives a function which needs to be called to create an instance.
The resulting object has a promise-like then() method that can be used
to detect when the module is ready. (We could use MODULARIZE_INSTANCE
to return the module directly as before, rather than the function,
but then we don't get the .then() method).

From 4a82d31e8cb808a04956fc847ed0ec0ff322b956 Mon Sep 17 00:00:00 2001
From: Hubert Chathi <hubert@uhoreg.ca>
Date: Wed, 3 Jan 2018 21:37:43 -0500
Subject: [PATCH] fix some typos in JavaScript library

Signed-off-by: Hubert Chathi <hubert@uhoreg.ca>

Make sure we null-terminate encrypted strings before passing them to
UTF8ToString.

This used to work when we allocated the buffer on the stack, because it turns
out that allocate() zeroinits the returned memory. malloc(), of course, does
not.

Avoid leaving copies of the plaintext sitting around in the emscripten heap.

Messages can be very large, so we don't really want to allocate them on the
stack. Switch to using the heap for them, and try to clean up some of the
string handling while we're at it.

If we get an exception during load, don't define half of window.Olm (which
confuses apps).

This is a partial fix to https://github.com/vector-im/riot-web/issues/2726.

Repeat the fix from b10f90d for megolm messages.

It turns out that the 'length' argument to 'Pointer_stringify' doesn't work if
the input includes characters >= 128.

Rather than try to figure out which methods can return UTF-8, and which always
return plain ascii, replace all uses of Pointer_stringify with a 'length'
argument with the version that expects a NULL-terminated input, and extend the
buffer by a byte to allow space for a null-terminator.

In the case of decrypt, we need to add the null ourself.

Fixes https://github.com/vector-im/vector-web/issues/2078.

I find myself wanting to know if an OlmSession is in the pre-key state or not,
to help debugging at the application level.

Ed25519 private keys, it turns out, have 64 bytes, not 32.

We were previously generating only 32 bytes (which is all that is required to
generate the public key), and then using the public key as the upper 32 bytes
when generating the per-message session key. This meant that everything
appeared to work, but the security of the private key was severely compromised.

By way of fixes:

 * Use the correct algorithm for generating the Ed25519 private key, and store
   all 512 bits of it.

 * Update the account pickle format and refuse to load the old format (since we
   should consider it compromised).

 * Bump the library version, and add a function to retrieve the library
   version, so that applications can verify that they are linked against a
   fixed version of the library.

 * Remove the curve25519_{sign, verify} functions which were unused and of
   dubious quality.

It turns out that the 'length' argument to 'Pointer_stringify' doesn't work if
the input includes characters >= 128.

Rather than try to figure out which methods can return UTF-8, and which always
return plain ascii, replace all uses of Pointer_stringify with a 'length'
argument with the version that expects a NULL-terminated input, and extend the
buffer by a byte to allow space for a null-terminator.

In the case of decrypt, we need to add the null ourself.

Fixes https://github.com/vector-im/vector-web/issues/1719.

Remove the (now non-functional) declarations of olm_set_log_level in the C and
js wrappers.

Output simpler JSON for the account keys, don't sign the JSON but instead provide a olm_account_sign method so that the user of the library can sign the JSON themselves

Rename axolotlpp as olm to avoid confusion with Axolotl-the-spec and Axolotl-the-OWS-libraries at moxie's request