Finally, after the long laziness, I have released the SDK for both custom edition and original version. They include source codes and fgd files. fgd files have entities which use more features of trinity. Entities will be explained in tutorials section. Check the section often for tutorials!
Also, I have finally provided the download link for the Version 3.08f of original trinity, which is the latest version of original trinity. So, developers who like plain trinity will be able to use the latest version with lots of more bug fixes.
Also, note that SDK for custom edition will not work with original and SDK for original will not work with custom edition.
Thanks for reading!