[fpc-pascal] JSON implementation

[Michael Van Canneyt]

Hi,

For those that need JSON support (JavaScript Object Notation), I committed
a hopefully complete implementation to packages/fcl-json. It contains demo 
programs and a fpcunit testsuite. There is a TJSONConfig component, similar 
to the TXMConfig component that comes with the XML implementation in fcl-xml.
(it's a component, so it could be included on the Lazarus component palette)

With this it should be pretty straightforward to implement a 
TJSONReader/TJSONWriter pair to plug in the component streaming system.

If you spot any bugs, or have remarks on how to improve it, I'd love to hear 
about it.

Enjoy!

Michael.