doc: add inheritance links and other changes

* README.md:
  * Change indentation to reflect class hierarchy.
  * Link to new doc/hierarchy.md which shows full class hierarchy.
* Add single sentence with link to parent class at the top of class doc.
* doc/addon.md:
  * Replace `Addon` with `Addon<T>`.
  * Show templating in prototypes.
  * Move `InstanceWrap<T>` method documentation to its own file, because
    it is shared with `ObjectWRap<T>`, and link to said new file.
* doc/array.md: Create the file from the `Array`-related contents of
  doc/basic_types.md.
* Remove doc/basic_types.md, splitting its contents per-class into
  individual files.
* Add doc/hierarchy.md, with full class hierarchy.
* Add doc/instance_wrap.md for documenting `InstanceMethod`,
  `InstanceAccessor`, and `InstanceValue`.
* Create doc/name.md from doc/basic_types.md, documenting `Napi::Name`.
* doc/object_wrap.md:
  * Add templating notation `Napi::ObjectWrap<T>`.
  * Show templating in prototypes.
  * Wrap file to 80 columns.
  * Remove methods provided by `InstanceWrap<T>` and link to
    doc/instance_wrap.md.
* doc/value.md:
  * Merge documentation from doc/basic_types.md.
  * Add namespacing.
  * Sort methods alphabetically.

Signed-off-by: Gabriel Schulhof <gabriel.schulhof@intel.com>
Fixes: #796
PR-URL: #798
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Nicola Del Gobbo <nicoladelgobbo@gmail.com>

README.md

@@ -81,28 +81,29 @@ The oldest Node.js version supported by the current version of node-addon-api is
 
 The following is the documentation for node-addon-api.
 
+ - [Full Class Hierarchy](doc/hierarchy.md)
  - [Addon Structure](doc/addon.md)
- - [Basic Types](doc/basic_types.md)
-    - [Array](doc/basic_types.md#array)
-    - [Symbol](doc/symbol.md)
-    - [String](doc/string.md)
-    - [Name](doc/basic_types.md#name)
-    - [Number](doc/number.md)
-    - [Date](doc/date.md)
-    - [BigInt](doc/bigint.md)
-    - [Boolean](doc/boolean.md)
+ - Basic Types:
     - [Env](doc/env.md)
-    - [Value](doc/value.md)
     - [CallbackInfo](doc/callbackinfo.md)
     - [Reference](doc/reference.md)
-    - [External](doc/external.md)
-    - [Object](doc/object.md)
-        - [ObjectReference](doc/object_reference.md)
-        - [PropertyDescriptor](doc/property_descriptor.md)
+    - [Value](doc/value.md)
+        - [Name](doc/name.md)
+            - [Symbol](doc/symbol.md)
+            - [String](doc/string.md)
+        - [Number](doc/number.md)
+        - [Date](doc/date.md)
+        - [BigInt](doc/bigint.md)
+        - [Boolean](doc/boolean.md)
+        - [External](doc/external.md)
+        - [Object](doc/object.md)
+            - [Array](doc/array.md)
+            - [ObjectReference](doc/object_reference.md)
+    - [PropertyDescriptor](doc/property_descriptor.md)
  - [Error Handling](doc/error_handling.md)
     - [Error](doc/error.md)
-    - [TypeError](doc/type_error.md)
-    - [RangeError](doc/range_error.md)
+      - [TypeError](doc/type_error.md)
+      - [RangeError](doc/range_error.md)
  - [Object Lifetime Management](doc/object_lifetime_management.md)
     - [HandleScope](doc/handle_scope.md)
     - [EscapableHandleScope](doc/escapable_handle_scope.md)