Split the json_view feature page into sub-pages (#6018)

* Split the json_view feature page into sub-pages

The single features/json_view.md page grew to ~600 lines covering eight
topics. Split it into features/json_view/ with an overview page and
pages for ownership and lifetime, differences from basic_json, reading
values, generic code, editing, and images.

The new differences page collects what was spread over several sections
("What is the same", "What is different", "Duplicate keys", and notes in
the conversion and serialization sections) under one summary table, and
adds the parts of the basic_json interface a view does not have. The
other pages now link to it instead of restating the rules.

Internal links across the documentation point to the new pages.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Docs: fix stale comments and trim repeated text in json_view pages

- fig-jsonview.js/.css: point the header comments at the new pages
- reading.md: views' strings are valid as long as the document (and a
  borrowed source text), as lifetime.md says
- reading.md, generic_code.md: link to differences.md instead of
  restating the member-order and repeated-key rules
- differences.md: drop the third mention of ordering comparisons, name
  rbegin()/rend() in the iterator row
- exceptions.md: link editable documents to editing.md

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/mkdocs/docs/home/exceptions.md

@@ -438,7 +438,7 @@ A UBJSON or BJData high-precision number could not be parsed.
 ### json.exception.parse_error.116
 
 [`basic_json_document::load()`](../api/basic_json_document/load.md) rejected an
-[image](../features/json_view.md#images): either the bytes are not one [`save()`](../api/basic_json_document/save.md)
+[image](../features/json_view/images.md): either the bytes are not one [`save()`](../api/basic_json_document/save.md)
 could have written (too short, an unknown magic number or format version, or sizes that do not fit the buffer), or
 they are, but fail the requested [`image_check`](../api/basic_json_document/load.md#image_check).
 
@@ -450,7 +450,7 @@ they are, but fail the requested [`image_check`](../api/basic_json_document/load
 
 !!! note
 
-    This exception was added in version 3.13.0, together with [images](../features/json_view.md#images).
+    This exception was added in version 3.13.0, together with [images](../features/json_view/images.md).
 
 ## Iterator errors
 
@@ -889,12 +889,12 @@ from JSON text.
 
 !!! note
 
-    This exception was added in version 3.13.0, together with editable [`json_document`s](../features/json_view.md).
+    This exception was added in version 3.13.0, together with editable [`json_document`s](../features/json_view/editing.md).
 
 ### json.exception.type_error.320
 
 [`basic_json_document::save()`](../api/basic_json_document/save.md) cannot write an
-[image](../features/json_view.md#images) of a [discarded](../api/basic_json_document/is_discarded.md) document.
+[image](../features/json_view/images.md) of a [discarded](../api/basic_json_document/is_discarded.md) document.
 
 !!! failure "Example messages"
 
@@ -904,7 +904,7 @@ from JSON text.
 
 !!! note
 
-    This exception was added in version 3.13.0, together with [images](../features/json_view.md#images).
+    This exception was added in version 3.13.0, together with [images](../features/json_view/images.md).
 
 ### json.exception.type_error.321
 
@@ -1192,7 +1192,7 @@ so they do not support an input of 4294967280 bytes (4 GiB minus 16 bytes) or mo
 storage: [`set`](../api/basic_json_document/set.md) and [`push_back`](../api/basic_json_document/push_back.md) throw
 this exception once the strings and number tokens written by edits reach 4 GiB in total, or once more than
 4294967295 arrays/objects have had an element set or appended to them. The same limit applies to an
-[image](../features/json_view.md#images): [`save()`](../api/basic_json_document/save.md) throws it if the node
+[image](../features/json_view/images.md): [`save()`](../api/basic_json_document/save.md) throws it if the node
 count, the text, or the decoded strings it would write would individually reach 4 GiB.
 
 !!! failure "Example messages"
@@ -1209,7 +1209,7 @@ count, the text, or the decoded strings it would write would individually reach
 
 !!! note
 
-    This exception was added in version 3.13.0, together with [`<nlohmann/json_view.hpp>`](../features/json_view.md).
+    This exception was added in version 3.13.0, together with [`<nlohmann/json_view.hpp>`](../features/json_view/index.md).
     [`basic_json::parse()`](../api/basic_json/parse.md) has no such limit.
 
 ## Further exceptions