[Lazarus] JSON SAX-based reader

[Michael Van Canneyt]

Hello,

I have changed the JSON parser, it is now written on top of a SAX-like JSON
reader (which is available separately). All unit tests work fine, and the
few extra tests which I did also, but I would like to hear if someone has
code that no longer works.

The change is committed in trunk. The new JSON reader is available in the
unit jsonreader. Useful if you want to process large amounts of JSON data
without building the whole JSON document in memory.

Michael.