lib: json-parser - Insert properly escaped unicode

lib: Add ostream-escaped filter

lib: JSON parser can now optionally parse input that isn't an object. Based on patch by Aki Tuomi.

lib: Added json_append_escaped_data() to escape non-NUL terminated input.

lib: json_append_escaped() doesn't need to escape the 8bit chars. We'll assume that the input is valid UTF-8.

Added json_append_escaped()

JSON parser: Added support for arrays. The parser should be complete now.

JSON parser: Added json_parse_skip_next() to skip over unwanted values.

JSON parser: Added support for reading string value as istream.

JSON parser supports now nested objects and parsing from non-blocking input stream.

Added a simple JSON parser for parsing an object.