Prevent name clashes when using multiple services that happen to have identical named items

Problem:
When using multiple services in one project that happen to have identical named items, identical named structures and functions are generated in identical named files, but with specific content for the different services. This can not be linked.

Solution:
Add an optional command line option to the generator application that adds a prefix to every filename, structure, function, typedefinition, etc... of a specific code generation session. This allows the developer to generate unique c-code for each service.

Example scenario:

• an application needs to use two services - let's call their
  respective wsdl files Mapping.wsdl and Geocoding.wsdl
• both services use a type called Coordinate, but it's not the same type
• upon generating C code from the wsdl files using WSDL2C, we get
  two adb_Coordinate.c and two adb_Coordinate.h files (one for each wsdl),
  with two adb_Coordinate_create(const axutil_env_t* env) functions etc.
• this leads to linkage errors