Add unittests for bridgedb.parse.addr module.
Add glossary definitions to bridgedb.parse.addr module docstring.
Add __future__ imports to bridgedb.parse.addr.
Remove except handler which never gets executed in bridgedb.parse.addr.
Numerous docstring improvements to bridgedb.parse.addr module.
Do not check IP validity in parse.addr.isIPv4() and parse.addr.isIPv6().

We only want to know if it is IPv4 or IPv6, *not* if it conforms to all kinds
of crazy routing RFCs.
Remove `return` statement which is never executed in parse.addr._isIPv().
Refactor addr.isValidIP() to give the reason for invalidity.
Return the port if it passes addr.PortList._sanitycheck().

This ensures that the return value has truthiness.
Stop parsing immediately if there is an invalid port in an addr.PortList.

This ensures that an addr.InvalidPort exception is raised when an invalid port
is discovered, without continuing to parse the rest of the ports. The end
result, i.e. when/if an exception is raised, stays exactly the same. This just
operates more efficiently when there is a bad port number.
Don't add duplicate ports to an addr.PortList.
Remove an unexecuted `except` branch from addr.PortList.add().
Change parameter `x` → `port` in addr.PortList.__getitem__().
Refactor unittests for bridgedb.parse.networkstatus.parseRLine().
Add unittests for bridgedb.parse.networkstatus.parseALine().
Add unittests for bridgedb.parse.networkstatus.parseSLine().
Add class variable docs to ParseNetworkstatusRLineTests unittests.

 * ADD documentation on default variables and how the unittest setup methods
   are used.
Document the `fingerprint` parameter in networkstatus.parseALine().
Remove one EOL whitespace in networkstatus module docstring.
Move constant ALPHANUMERIC into function isValidRouterNickname().

It isn't used anywhere else, and it would be silly to import it from
here, so there is no reason to have it at the module level.