Update docs on io_scheduler for inline processing (jbaldwin#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

coro::mutex uses function for unlocked state to reduce memory (jbaldw…

…in#77)