Release 1.5.0

[kerrizor]

Lots of new stuff in 1.5.0! We've gotten Rails 5.x support in place, as
well as adding 2 new options. "clustering" will draw a box around models
contained in the same name space, helping to visually organize areas of
concern. "only_models_include_depth" - although awkwardly named - will
restrict the depth of graphing to the supplied value.

• New option of 'clustering' by namespace (Implement clustering by namespace #205)
• Support for 'only_models_include_depth' option (support for 'only_models_include_depth' option #219)
• Added basic support for non-Rails apps (Add supports to non Rails apps. #208)
• Avoid duplicate specializations when using STI with an abstract base class (Avoid duplicate specializations when using STI with an abstract base class #211)
• Fixed Ruby 2.1 deprecation warnings (Fix deprecation of File.exists? #209)
• Fixes to tests (Avoid warnings when redefining methods in tests. #210, Skip resetting ActiveRecord::InternalMetadata, which breaks all tests for Rails 5 #213)
• Various documentation fixes (Updated diagram options (indirect -> direct) #203, Mention Rails 5 in README #212)