Tests and fixes

[githubDante]

Covered by the tests:

• both PySolarman versions
• read of input/holding registers and coils (sync)
• skipping of counter packets
• auto reconnect

Fixes:

• as discussed in #34 the reader thread and all attributes used by it are needed only if self.sock is a socket object
• small changes in the auto-reconnect logic for issues spotted during testing

New:

• disconnect method for the async version
• NoSocketAvailableError is raised on empty response from the data logger

[githubDante]

The idea is good. What about this implementation ?!?

[jmccrohan]

@githubDante LGTM. Will merge now.