Replace the init-static-var dance with some preprocessor macros

We never delete a cipher, and the destruct op is empty, so it's a bit pointless

Give a load of internal symbols "_olm_" prefixes. This better delineates the
public and private interfaces in the module, and helps avoid internal symbols
leaking out and possibly being abused.

Should have been in the previous commit :/

These seem to be the wrong way around.

So that we can build everything together.

Split the python wrappers into separate modules

We want to stop aes_* and sha_* functions leaking out of our .so, as well as
internal _olm_* symbols.

This also means we need to link the unit tests against the objects. Possibly we
should distinguish between unit tests and integration tests.

Now that we have C and C++, we need to split the compile and link steps
(because we need different flags for the C and C++ files), so this is
easier with a Makefile.

Replace the python scripts for building the shared lib and tests with a
Makefile, which makes it easier to handle a mix of C and C++.

We don't want anything which does dynamic memory allocation in the library.

* We only use 8-byte MACs
* The version byte is \x03, not \x01

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

Concerns have been raised that including logging functionality makes it harder
to audit the implementation to ensure that no secret information is leaked. We
are therefore removing it from the master branch.