Prepare for Erlang/OTP 22

Fix dialyzer errors

Fix for incorrectly counting dropped messages

Retry strategy for flaky tests

Lager changes the error level of supervisor progress messages from
info to debug. This is done after the hwm checking changes the received
message count. This PR implements a fix by removing one from the count
if no message was sent.

Closes: #496

fix the pr_stacktrace invocation example

Fix rotation on Windows

Windows requires that file handles be closed prior to renaming files. In
addition, the inode on non-Unix OSes is always zero. This PR closes the
log files prior to rotation (instead of after) and ensures the case
where the file descriptor is `undefined` is handled.

Document error_logger_whitelist and other updates

Closes #363

Maybe remove OTP 21 logger default handler

Closes #481

Remove check for erlang:is_map/1

Handle errors generated by cowboy which were treated as ranch errors

c998673eb0/src/cowboy_stream_h.erl (L153-L157)

Improve debug tracing support

Check for the right number of dropped messages

By an unhappy accident, OTP21 added functionality for 'named' trace
functions. This has a pattern match that matches the old trace function
(a 2 tuple where the second element is itself a 2 tuple):

https://github.com/erlang/otp/pull/1781

This patch changes to using a versioned record (so we can extend the
tracing later if needed) and adds 3 more options to tracing; count,
timeout and format string.

Additionally, tracing an OTP process via start_link arguments is now
documented.

Was 16, is now 15 after we merged #475

Fix check_hwm

replace list comprehension with recursive invokation in pr/2

The list comprehension fail on improper lists, use a recursive
call into pr/2 instead.

Fixes #477.

During further testing found one more bug in check_hwm
This fix is an addition to https://github.com/erlang-lager/lager/pull/467

Handle strange crash report from gen_statem

Prior to this change, lager would simply rename all the files and leave
the 'base' filename empty until a log event came into create it. This
caused confusion with users and tooling.

The fix, as suggested by Shamis Shukoor, is to not delete/rename the
base file, but simply try to open it in write only mode. This will
create the file if it does not exist and truncate it if it does.

Co-authored-by: Shamis Shukoor <shamis657@gmail.com>

Prevent silent dropping of messages when hwm is exceeded

is_loggble - support for severity as atom