Add macron submodule

• Add new macron submodule to implement mir.Engine backend by Macaron engine

Fixed error when register entries by iris/mux and optimized test case

• Add ginkgo style test case for mir module and sub-module(gin,echo,httprouter,mux)
• iris: add iris httptest style test case
• Fixed some error when register entries to engine(iris/mux)
• Optimized mir core code logic and mir.Chain can defined but not assign

Fixed error when mir.Chain field defined but no assign

• Support defined mir.Chain field but no assign when init entry to register

Add Echo,Iris,httprouter as backend for mir.Engine implement

• Add echo sub-module provide mir.Engine implement backend by Echo
• Add httprouter sub-module provide mir.Engine implement backend by httprouter
• Add iris sub-module provider mir.Engine implement backend by Iris

Support set custom tag name for mir

• Add mir.SetTag(...) function to custom struct tag of mir to parse handler info from struct field

Support register middleware to engine defined by mir.Chain type

• Support register middleware to engine defined by mir.Chain type
• Optimized group info define,can direct assign group string to mir.Group field override default group info in mir tag string
• Add mux sub-module to implement mir.Engine backend by Mux

support direct register entries with give engine

• add SetDefault(...)/RegisterDefault(..) function
• change Register(...) function with a mir.Engine argument to direct register entries with engine instance
• change mir.Engine interface define

First release version of mir

• Add core logic to reflect handler, path, method, queries, group info from mir tag string
• Add gin sub-module to implement mir.Engine backend by Gin