Add init language documentation

doc/language/README.md

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+# Features
+
+mruby is an implementation of the Ruby programming language.
+These documents are describing the language features and libraries
+which are provided together with mruby.
+
+## Core Classes and Modules
+
+### Array
+
+The class Array is an implementation of the Array data type in Ruby
+
+[Wikipedia - Array data type](http://en.wikipedia.org/wiki/Array_data_type)
+> In computer science, an array type is a data type that is meant to describe
+> a collection of elements (values or variables), each selected by one or
+> more indices (identifying keys) that can be computed at run time by the
+> program.
+
+#### Methods
+
+##### *
+
+##### +
+
+##### <<
+
+##### []
+
+##### []=
+
+##### clear
+
+##### concat
+
+##### delete_at
+
+##### empty?
+
+##### first
+
+##### index
+
+##### initialize_copy
+
+##### join
+
+##### last
+
+##### length
+
+##### pop
+
+##### push
+
+##### replace
+
+##### reverse
+
+##### reverse!
+
+##### rindex
+
+##### shift
+
+##### size
+
+##### slice
+
+##### unshift
+
+##### inspect
+
+##### to_s
+
+##### ==
+
+##### eql?
+
+##### <=>
+
+### Class
+
+### Comparable
+
+### Enumerable
+
+### Hash
+
+### Numeric
+
+### Object
+
+### Proc
+
+### Range
+
+### String
+
+### Symbol
+
+## Standard Library