Merge branch 'appveyor-cmake-v6'

This patch set introduces matrix for appveyor and fixes bugs related to win32,
during debugging this matrix. This should greatly reduce number of work for
making a release ('check under windows' part only).

Right now tests on appveyor still failes in summary, but we should dig into
problems, not hide them.

Test matrix looks like this:
- autotools
- autotools --disable-openssl
- autotools --disable-thread-support
- autotools --disable-debug-mode
- autotools --disable-malloc-replacement
- cmake
- cmake -DEVENT__DISABLE_OPENSSL=ON
- cmake -DEVENT__DISABLE_THREAD_SUPPORT=ON
- cmake -DEVENT__DISABLE_DEBUG_MODE=ON
- cmake -DEVENT__DISABLE_MM_REPLACEMENT=ON
- cmake -DEVENT__ENABLE_VERBOSE_DEBUG=ON
- cmake -DCMAKE_C_FLAGS='-DUNICODE -D_UNICODE'
And takes 90min (was 7min, and this is the sad part).

* appveyor-cmake-v6:
  test/ssl: use send()/recv()/EVUTIL_ERR_RW_RETRIABLE()/EVUTIL_SOCKET_ERROR() to fix win32
  test/https_basic: increase timeout for complete write (fixes win32)
  cmake: check for ZLIB_INCLUDE_DIR, since we can have only library without headers
  autotools/win32: fix searching ssl library
  appveyor/autotools: link with openssl by passing LDFLAGS/CFLAGS
  appveyor: image already had openssl installed
  cmake/win32: do not compile regress_thread on -DEVENT__DISABLE_THREAD_SUPPORT=ON
  cmake/win32: do not compile evthread_win32 on -DEVENT__DISABLE_THREAD_SUPPORT=ON
  appveyor: check -DUNICODE -D_UNICODE according to ReleaseChecklist (cmake only)
  cmake: fix -DEVENT__ENABLE_VERBOSE_DEBUG (typo on -DUSE_DEBUG)
  test: fix building with --disable-thread-support under win32
  cmake: do not use stderr for notifications/version-info
  autoconf: fix --disable-thread-support build under win32
  appveyor: ignore failure of mingw-get
  appveyor: drop shallow_clone, since we use tags for detecting version in cmake
  appveyor: support cmake & autotools using build matrix (like travis-ci has)

Fixes: #364