2.0.0 changelog

- all lengths now 4/8, 6/8, 8/8, 10/8, or 12/8
    - easy to make tile length trains
    - or don't bother
- depot flip enabled in many cases
    - Iron Horse 1 couldn't do this
- cargos
    - updated cargo support for FIRS etc
    - better default choices when first default isn't available (climates, FIRS economies)
- reworked the entire tech tree
    - see gameplay guide
    - 6 generations (date range??)
    - clear distinction between engine roles
    - many engines added
        - still aim to keep one obvious choice per route, but with a wider spread of engines
    - much more comprehensive electric engine roster
    - many more types of passenger, mail and freight wagons
        - list types added
        - vehicles, intermodal and supplies cars are missing from v2 vs v1, may be restored in future
    - full set of railcars
    - high speed and very high speed trains
    - some engine names kept for continuity with v1, the rest renamed
    - removed combine cars, they don't work with autoreplace 
    - reset capacities so that wagon length is purely a visual choice
    - rebalanced speeds, weights, costs, vehicle expiry dates etc
- reworked all sprites
    - livery options
        - see gameplay guide
- updated visual effect handling
    - more accurately positioned visual effects
    - rear lights on consists
    - electric engine pans are dropped / raised if on elrl (or not)
    - doors open on many vehicles when loading/unloading
- translations
- buy menu information for trains
- docs updated
    - improved display of trains
    - better navigation
- super rework of much code
    - faster compiles
    - no longer everything articulated
    - revamped graphics generation
        - automated buy menu sprites
        - automated cargo sprites
        - automated chassis and roofs
        - automated pantographs
    - shared library of cargo sprites, cargo refits etc with Road Hog and Unsinkable Sam
    - much refactoring
    - etc