* raimo/receive-TOS-TCLASS/ERIERL-187/OTP-15145:
  Write testcases for recvtos and friends
  Fix term buffer overflow bug
  Fix documentation due to feedback
  Implement socket option recvtos and friends

When a handler process is terminated due to overload, it reads its
configuration from the configuration database, so it can be restarted
with the same configuration after a small delay. This was earlier done
in a different process, which was spawned off from the terminate
function. This caused a race condition, where in some cases, the
configuration was already removed before it could be read.

The reason for spawning off a process, is to avoid a deadlock due to
the call to logger:remove_handler/1.

This commit moves the call to logger:get_handler_config/1 back to the
handler process - to ensure that the data is still there, but keeps
the call to logger:remove_handler/1 in the spawned off process - to
avoid deadlock.

If the report callback function has two arguments, the second argument
is a map with options to limit the size of the log event. To even
allow a better formatting when the event shall be printed on a single
line, the new option single_line is now included in this
argument.

If a filter fails, it is removed by a call to
logger:remove_filter/1,2. If the log event that caused the failure was
issued on the logger process itself, this would earlier cause a
deadlock due to a gen_server:call to self(). This is now prevented.

The encoding option was introduced in commit
270d909696a753af022df72a404c73f2895b4a02, to allow report callbacks to
format according to a given encoding. There was, however, no
connection between this encoding option, and the encoding of the
device to which the logger handler was writing.

Since a formatter is defined to return unicode:chardata(), and in
order to avoid mismatch with the encoding of the device, the encoding
option is now removed from the formatter. The handler itself must make
sure that it does not write illegal data to its device.