Update catch2 to v3

#113

#110 Fix exception throwing in coroutines

#110 Fix exceptions being thrown at the wrong point in coroutines

io_scheduler thread_pool OR inline task execution

Update docs on io_scheduler for inline processing (#84)

* Update docs on io_scheduler for inline processing

Support gcc 10.3.1 (fedora 33 updated)
Update ci.yml to run fedora 32,33,34 and support both
gcc 10.2.1 and 10.3.1

* fedora 32 -> gcc-c++ drop version

* Update ci.yml and test_latch.cpp

Initial pre-release

Basic coroutine constructs for C++20 along with thread_pool, io_scheduler and tcp client/server with SSL support.