Allow disabling the AppAuthor directory on Windows.

[dstufft]

I haven't actually tested this on Windows as I don't have easy access to one with Python setup at the moment. However I'm fairly sure this is correct.

This is part of #40

[srid]

this is what i saw on Windows 8:

C:\Users\Sridhar\Documents\GitHub\appdirs [master +0 ~1 -0]> python .\appdirs.py
-- app dirs (with optional 'version')
user_data_dir: C:\Users\Sridhar\AppData\Local\MyCompany\MyApp\1.0
site_data_dir: C:\ProgramData\MyCompany\MyApp\1.0
user_config_dir: C:\Users\Sridhar\AppData\Local\MyCompany\MyApp\1.0
site_config_dir: C:\ProgramData\MyCompany\MyApp\1.0
user_cache_dir: C:\Users\Sridhar\AppData\Local\MyCompany\MyApp\Cache\1.0
user_log_dir: C:\Users\Sridhar\AppData\Local\MyCompany\MyApp\1.0\Logs

-- app dirs (without optional 'version')
user_data_dir: C:\Users\Sridhar\AppData\Local\MyCompany\MyApp
site_data_dir: C:\ProgramData\MyCompany\MyApp
user_config_dir: C:\Users\Sridhar\AppData\Local\MyCompany\MyApp
site_config_dir: C:\ProgramData\MyCompany\MyApp
user_cache_dir: C:\Users\Sridhar\AppData\Local\MyCompany\MyApp\Cache
user_log_dir: C:\Users\Sridhar\AppData\Local\MyCompany\MyApp\Logs

-- app dirs (without optional 'appauthor')
user_data_dir: C:\Users\Sridhar\AppData\Local\MyApp\MyApp
site_data_dir: C:\ProgramData\MyApp\MyApp
user_config_dir: C:\Users\Sridhar\AppData\Local\MyApp\MyApp
site_config_dir: C:\ProgramData\MyApp\MyApp
user_cache_dir: C:\Users\Sridhar\AppData\Local\MyApp\MyApp\Cache
user_log_dir: C:\Users\Sridhar\AppData\Local\MyApp\MyApp\Logs

-- app dirs (with disabled 'appauthor')
user_data_dir: C:\Users\Sridhar\AppData\Local\MyApp
site_data_dir: C:\ProgramData\MyApp
user_config_dir: C:\Users\Sridhar\AppData\Local\MyApp
site_config_dir: C:\ProgramData\MyApp
user_cache_dir: C:\Users\Sridhar\AppData\Local\MyApp\Cache
user_log_dir: C:\Users\Sridhar\AppData\Local\MyApp\Logs
C:\Users\Sridhar\Documents\GitHub\appdirs [master +0 ~1 -0]>