Allow blank value for LocationField.
Merge branch 'master' into allow_blank_value

Conflicts:
	location_field/widgets.py
Added missing import to the example in README. Fixes #7
Merge pull request #6 from Kami/allow_blank_value

Allow blank value for LocationField. Thanks to @Kami
Load google maps JavaScript file from https URL, otherwise it won't work on ssl
enabled websites with modern browsers (e.g. Chrome).
Use a schemaless url instead.
Merge pull request #8 from Kami/fix_javascript_source_issue

Using schemaless URL to load google maps javascript.