Windows support

[spenceforce]

Currently pdb-attach only support linux.

[spenceforce]

Windows support will probably require a different implementation since os.kill does not have the same functionality seen in Python for Linux.

[AlucardNosferatu]

module 'signal' has no attribute 'SIGUSR2'

[spenceforce]

This package uses signals to initiate the socket connection that allows pdb to interact with the client. Unfortunately signals on Windows don't work the same as on POSIX, so for the time being this package can't be used on Windows platforms. Adding Windows support will require a different implementation that doesn't use signals. To mitigate this confusion, I will make this package throw an exception when imported on Windows.