libevent examples: Fully convert to libevent2 (issue #5)

Currently, unfortunately some of the libevent-based examples would not
compile at all, others would compile but crash immediately because they
were mixing libevent and libevent2 calls.

This problem was kindly pointed out (for libevent-demo) by
otisman32 @ github.
tests/: Modify not to rely on system-installed libgtest

This allows building testsuite even without root access and even with
simply installing the libgtest-dev package on Debian-alike systems.
pubnub_finished_cb(): New finished_cb wrapper that cleans up beforehand

In some places, e.g. resubscribe_http_init(), we look at whether
p->finished_cb_data holds anything, and if there are leftovers from
a previous call (e.g. here_now), things blow up.  Therefore, we make
sure that at the point when we issue the callback, there are no
leftovers.

This fixes specifically a crash when we issue here_now and from
its callback perform a subscribe. here_now is one of the few functions
that have no callback wrapper that'd clean up finished_cb_data, and
the subscribe eventually descends to a resubscribe call, which looks
at finished_cb_data and from its existence it judges that we just
interrupted an ongoing subscribe.

So we now fulfill its implicit assumption that finished_cb_data is
always a NULL when there's no call in progress.
libpubnub-1.0: First stable release of the libpubnub API

This seems as good a moment as any, as our library seems to be gathering
non-trivial deployment.

We expect not to fix ourselves on the "1.0" version number overly; this
version indicator serves only to distinguish API/ABI compatibility and
we will bump it whenever we need to break something.  If we ever need
to make a truly major overhaul of the library, we'll probably call that
libpubnub2 or something.

In short, marking this as 1.0 is just a convenience for our users and
a stable reference point.

We also introduce PUBNUB_APIVER_MAJOR / PUBNUB_APIVER_MINOR #defines
in pubnub.h along this.
Append pnsdk query parameter to all HTTP requests
libpubnub/pubnub.h [serialization]: Improve function descriptions
[serialization]: Also keep the resume_on_reconnect flag
tests/: Adjust to the previous commit (introducing ?pnsdk)
Merge branch 'master' into develop

Conflicts:
	tests/pubnubtest.cpp
PubnubTest [serialization]: Test a full URL at least once
[serialization]: Always generate the channels attribute, even if it's just []
[serialization]: Expand documentation on sanity assumptions
[serialization]: Expand documentation on what is and isn't serialized