Improved RPC library with added bounds checking to stop memory corruption, removed memory leaks, Arduino pin names, better object discovery.

Fork of mbed-rpc by mbed official

I have added bounds checking in both Argument and Reply classes to stop existing buffer over-runs in both classes.

Added the ability to discover the name and class of an RPC object to allow better discovery of existing objects on a server. Removed a memory leak with externally created RPC objects. Ensured consistency so that externally created objects can't be deleted using the RPC interface and are correctly listed after RPC::clear.

Updated RPCVariable to use references instead of pointers to ensure that the compiler checks that there is always a valid backing variable. Also removed RPC new/delete functionality as this is not valid. Added a specialisation of RPCVariable to allow for strings to be read and written via RPC.

Added Arduino pin names to parse_pins, currently only for FRDM boards but same code should work for others just need to add them to the #ifdef.