Added a new location setting, allowing the breadcrumb to be applied to a specific menu.
    If the location setting is empty, default to the first menu seen.
    Should improve theme compatibility for themes that do not use the TwentyXX naming conventions.
        Added default value (empty string) for the new location setting.
        Added new location setting to the admin menu.
        Change the primary menu detector code to look for a matching location, or for the first callback used.
        Updated readme with autolocation functionality.
        Updated test cases for new location setting field.
        Added additional location tests for debug-enabled test cases.

git-svn-id: https://plugins.svn.wordpress.org/instant-breadcrumbs/trunk@880680 b8457f37-d9ea-0310-8a92-e5e31aec5664