Fixes#71, #93, #158, #168, #209, #141, #160, #162, #190
* Fixed: indentation in comment
* Fixed: Get() returns nil when nested element not found
* Fixed: insensitiviseMaps() made recursive so that nested keys are lowercased
* Fixed: order of expected<=>actual in assert.Equal() statements
* Fixed: find() looks into "overrides" first
* Fixed: TestBindPFlags() to use a new Viper instance
* Fixed: removed extra aliases from display in Debug()
* Added: test for checking precedence of dot-containing keys.
* Fixed: Set() and SetDefault() insert nested values
* Added: tests for overriding nested values
* Changed: AllKeys() includes all keys / AllSettings() includes overridden nested values
* Added: test for shadowed nested key
* Fixed: properties parsing generates nested maps
* Fixed: Get() and IsSet() work correctly on nested values
* Changed: modifier README.md to reflect changes
