Merge pull request #112 from Qingtao-Cao/devel

First round of bug fixes
Finalised document

As per.
Merge pull request #114 from Qingtao-Cao/devel

Have mg_adaptor skip over off-lined devices.
Revert "Have mg_adaptor skip over off-lined devices."

This reverts commit 7f29bbd9f4b3826307063ff0cdb66c84c8688ecf.

IT admins would favour the idea not having to have them send USR1
signals to mark a device on-lined once it gets re-installed properly.
To this end the previous behaviour of the mg_adaptor is preserved
except that no error logs about "Connection timed out" for off-lined
devices are generated.
Disable error logging for off-lined devices in mg_adaptor

Have mg_adaptor generate error logging for off-lined devices once
so as to prevent polluting logs. However, the collector thread
on a particular modbus line will still try to read from off-lined
device so that their status can be picked up as soon as they are
on-lined.