Reorganize directories (#3462)

* 🚚 move files
* 🚚 rename doc folder to docs
* 🚚 rename test folder to tests

docs/mkdocs/docs/api/json_sax/parse_error.md

@@ -0,0 +1,28 @@
+# <small>nlohmann::json_sax::</small>parse_error
+
+```cpp
+virtual bool parse_error(std::size_t position,
+                         const std::string& last_token,
+                         const detail::exception& ex) = 0;
+```
+
+A parse error occurred.
+
+## Parameters
+
+`position` (in)
+:   the position in the input where the error occurs
+
+`last_token` (in)
+:   the last read token
+
+`ex` (in)
+:   an exception object describing the error
+
+## Return value
+
+Whether parsing should proceed (**must return `#!cpp false`**).
+
+## Version history
+
+- Added in version 3.2.0.