Dynamic C extensions usage changes

In version 1.3x, you must use FGLPROFILE entries to specify Dynamic C extensions to be loaded at runtime.

In version 2.0x, Dynamic C extensions are automatically loaded according to IMPORT instructions. The FGLPROFILE entries are no longer used.

Important: Global variables (userData) can no longer be shared between the runtime system and the C extensions. You must use functions to pass global variable values.

There is no longer a need to define the FGL_API_MAIN macro in the extension interface file.

All C data type definitions are now centralized in the fglExt.h header file, header files like Date.h, MyDecimal.h have been removed from the distribution.