Release 3.1.0

CMake improvements (#369)

* Silence CMake warning by updating minimum versions.

* Generate files to build directory, not source directory

[WIP] use vcpkg for getopt; build windows shared lib enhancements (#350)

* fix MSVC compiler shared library issues - mostly around 'extern const'

* add vcpkg install getopt to appveyor-windows.yml

show appveyor where to get getopt from vcpkg (non-static lib to avoid LGPL violation)

* add missing else case in lsquic_shared_support.h for windows static lib path

* have cmake spit out it's version

have cmake copy dependent dlls to build dir for tests on windows (getopt.dll)

* copy getopt.dll dep for tests

added commented version that requires >= 3.21 but handles any dll deps

* try caching boringssl dir to reduce CI build time since it's always same commit specified in config file

define VCPKG_ROOT in env since I can't seem to find it by VCPKG_ROOT or VCPKG_INSTALLED_DIR in appveyor's cmake v3.16 + vcpkg

* make windows cache dependent on yml and cmd

* sync up with changes to ls-qpack

Release 2.29.1

- Make it possible to build the library and unit tests without
libevent.
- Build all command-line utilities in bin/
- Add perf_client and perf_server command-line utilities to test
performance according to the "perf" protocol.

Make libevent optional; move binaries into bin/

Release 2.27.1

- [API] New knob to set outgoing packet batch size.
- Aborted connection now become tickable immediately.
- Abort connection when HTTP/3 frame cannot be opened (can only happen
when malloc fails).

Release 2.19.10 -- Fix Windows and MacOS builds

Fix Windows support

Rename test/unittests to tests/ and test/ to bin/