Add .well-known support

Basic support for room upgrade handling.  Closes PR #18

Build lib as Shared Object

Build mtxclient as a shared object. No longer statically link boost libs during build.

Fix mismatch between new[] and delete with Olm objects.  Thanks @MonokelPinguin 

Fix CI issues w/ mtxclient.  Thanks to @MonokelPinguin 

Current AppVeyor image includes a very old vcpkg snapshot. Because of
that, this doesn't include https://github.com/Microsoft/vcpkg/pull/5258
specifically
https://github.com/Microsoft/vcpkg/pull/5258/commits/c895bb658d52bee471169460c711fdd90e3d5b7b

Because of that, find_package only works for find_package(nlohmann-json)
but not find_package(nlohmann_json). Updating the ports cache should fix
that.

Add missing iostream include.  Should hopefully fix #11 .  Thanks @MonokelPinguin 

Otherwise build breaks with boost>=1.70

Should fix #11

memory leaks in the implementation.

Workaround synapse bug #4898 Thanks @MonokelPinguin 

Ignore type_error while parsing timestamp of read receipts, because
Synapse sends out data for them, when using workers.

https://matrix.org/docs/spec/client_server/unstable.html#key-export-format

Currently, importing does not work.  Do not use this commit
if you intend to keep import/export working.  I also have not yet
cleaned up the code, so there might be some nasties that have
not been discovered.

I think I finally worked out the issues w/ linking against the
nlohmann JSON library.  I have updated the build and the various
CI scripts.

Fix Findsodium.cmake version test. (thanks @jevolk )