Add ability to specify a default location for settings file

[dkliban]

Users of Django apps have to specify a 'DYNACONF_SETTINGS' environment variable to specify where their settings file is located. Application writers would benefit from being able to set a SETTINGS config in their settings.py which would provide a default location for a settings file. If the file is not present, dynaconf should log this, and allow django to start up normally.

[rochacbruno]

Hi @dkliban I think this issue is related to #73

In your case when using Django I guess (need to test it) you can put in your settings.py

SETTINGS_MODULE_FOR_DYNACONF=/etc/foo.yml

Then this value would be the default unless it is overwritten by environment variable {PREFIX}_SETTINGS

[dkliban]

That worked for me! Thank you @rochacbruno