Add json parser

Signed-off-by: Alexey Gladkov <[email protected]>

docs/shell-json.md

@@ -0,0 +1,40 @@
+shell-json(3)
+
+# NAME
+
+json_foreach - function for streaming json parsing
+
+# SYNOPSIS
+
+- json_foreach
+- json_foreach_handler type value
+- json_get_last_name retvar
+- json_get_full_name retvar [separator]
+
+# DESCRIPTION
+
+## json_foreach
+The function consumes standard input to parse JSON and calls `json_foreach_handler` for each
+simple value (`string`, `number`, `boolean` and `null`).
+
+## json_foreach_handler
+The function is a callback that is called for each JSON value. The function
+receives the value type and the JSON value of the variable as arguments. Inside
+the callback, you can get the field name by calling the `json_get_last_name`
+or `json_get_full_name`.
+
+## json_get_last_name
+This is a helper that is meant to be called from the `json_foreach_handler`. It
+puts into the `retvar` with the name of JSON field.
+
+## json_get_full_name
+Same as `json_get_last_name` but returns full JSON field name. The name is made
+up of the parent names of the fields joined with a `separator`.
+
+# AUTHOR
+Authors and contributors of the programs included in the *libshell* package are listed
+in the COPYING file.
+
+# BUGS
+Report bugs to the authors.
+