Release 3.1.0

[MISC] replace TAB with 4 spaces.

[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 2.27.1

- [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).

Fix Windows support

Resuscitate Windows build (#61)

Merge wincompat/test_common_win.c into test_common.c

The macro soup in test_common.c acquired a few more fingernails, but
this is better than maintaining (or, rather, forgetting to maintain)
two versions of the same code.

[BUGFIX] Wincompat: use the new APIs (commit e8bd737db48)

updated to upstream ran all tests again.

compiles in debug/release. tests pass (in debug config at least)