mikroE provides libraries for USB HID, LCD, I2C, SPI, UART, MMC and many other things. If you download and install the mikroC PRO PIC demo Compiler and open it then at the right side of the app you will see the list of libraries. You can download more libraries from libstock.com and install it. These are compiled libraries. So, there will be no source code available for the libraries. If you want to see their code then compile it and view the .asm file and it will show asm code of the library.