c_glib: Support server implementation

The attached patches modify the C (GLib) compiler and library to add support for implementing servers.

The changes to the compiler include

• Adding server-generation methods
  • generate_service_helpers, which generates a pair of ThriftStruct subclasses for each service method, used to deserialize the method's arguments and serialize its result
  • generate_service_handler, which generates an abstract base class for a service's handler implementations
  • generate_service_processor, which generates a service's processor class

• Adding helper methods underscores_to_initial_caps and property_type_name which, respectively, convert an underscore-delimited name back to camel case and return the GLib type needed to store a Thrift type as a GObject property

Changes to the library include

• Changing the signature of ThriftProcessor.process so it returns I/O errors to its caller

• Adding the ThriftDispatchProcessor class, ported from the C++ implementation, which subclasses ThriftProcessor and parses an incoming method-call message for dispatch by subclasses

• Adding a peek method to ThriftTransport and corresponding implementations in ThriftSocket, ThriftBufferedTransport and ThriftFramedTransport

• Add ThriftBufferedTransportFactory and ThriftFramedTransportFactory, used by the server to wrap a raw ThriftTransport in the corresponding subtype

• Changing the signature of ThriftServer.server so it returns an error status to its caller, following GLib's conventions

• Changing ThriftSimpleServer.serve so it
  • Detects and reports errors encountered during processing
  • Uses transports returned by the transport factories instead of the (raw) transport passed in by the caller
  • Uses ThriftTransport.peek to detect the end of input
  • Returns an error status to its caller