json-cpp Code

- removed some warnings when compiling with gcc 4.1.

- added test to check empty member name { "" : 134 }.

- added some documentation
- added ValueAllocator to customize string duplication.

- updated build instructions
- integrated build instructions in html doc.

- added memory pool based allocator.

- added experimental StaticString support to avoid useless string duplication in Value constructor or member association.

- Value may now (optionally) use an internal hash-map and a simplified deque for objectValue and arrayValue storage.
- iterator related code extracted into src/lib_json/json_valueiterator.inl

- memory footprint of Json::Value is back to 16 bytes on WIN32.
(using bool allocated_:1 caused the compiler not to merge the attribute with the previous bitfield. Switched to int type to fix the problem).

- correct include path are now generated in the documentation.

- added (untested) accessors to get index or member name when iterating over members.