First of all I need to explain that Cosa is an object-oriented platform for Arduino with over 100+ classes. It is an Arduino core but supports all AVR processor based boards plus ATtiny and Mighty. It is also stand-alone and does not depend on any Arduino code more than the IDE build process.
The simplest example sketch is the LCD hello world that I use for footprint benchmarking.
The pin-out is described in the Board description file for ATtiny.
https://github.com/mikaelpatel/Cosa/blob/master/cores/cosa/Cosa/Board/TinyX5.hh#L41
Pins in Cosa are symbols, e.g. Board::D0 instead of integers as in Arduino/Wiring.
You can basically develop on Mega, Uno, etc, and simply select ATtiny85 and compile-and-burn with more libraries than in any other Arduino package. SPI, TWI, 1-Wire etc are all support. LCD support is an abstract class that is implemented for HD44780, PCD8544, ST7565. The HD44780 driver also has an adapter layer for 4-bit parallel, Shift Register 3-wire (Pin or SPI), Shift Register 4-wire and a whole range of different I2C adapters. You can see how the configuration works in the CosaLCDsize sketch above.
Cheers!
Mikael