Replace Boost.Asio with plain Asio

[tstenner]

Closes #143.

[cboulay]

It would also be good to get @chausner to look at this.

[chausner]

It would also be good to get @chausner to look at this.

Don't really have an opinion on this as I am not really familiar with those libraries. At least, I can't think of any reason that would speak against this change.

[tstenner]

@chausner The main parts that might be relevant to you (out of all the 352833 changed lines :-) are:

• Asio is included as #include <asio/ instead of #include <boost/asio, so unless …/include/boost/ is on the include path, no part of Boost.Asio is imported any more
• the Asio include path is added to the lslobj target, not lslboost
• -D_WIN32_WINNT=…, mswsock and ws2_32 are no longer needed for lslboost and can be moved to lslobj

Building the PR with MSVC (shared/static) didn't produce any new warnings that those flags were missing, but maybe there's something I have forgotten.

[tstenner]

Rebased and built successfully against the Android NDK