Fix .def and .sym files not being added to sources
Add GroupTargetSources module
Slight refactoring
Rewrite amxplugin.c in assembly
Move private sources to src/private/
Add ProductName and FileDescription fields
Use relative path for SAMPGDK_DEF_FILE and SAMPGDK_SYM_FILE
Use configure_file() to generate sampgdk.rc
Store path to version.h in SAMPGDK_VERSION_FILE