May 2018 release

New Levels:

1. DMLab-30.

   1. contributed/dmlab30/psychlab_arbitrary_visuomotor_mapping
   2. contributed/dmlab30/psychlab_continuous_recognition

2. Psychlab.

   1. contributed/psychlab/arbitrary_visuomotor_mapping
   2. contributed/psychlab/continuous_recognition

New Features:

1. Support for level caching for improved performance in the Python module.
2. Add the ability to spawn pickups dynamically at arbitrary locations.
3. Add implementations to read datasets including Cifar10 and Stimuli.
4. Add the ability to specify custom actions via 'customDiscreteActionSpec' and
   'customDiscreteAction' callbacks.

Bug Fixes:

1. Fix playerId and otherPlayerId out by one errors in 'game_rewards.lua'.
2. Require playerId passed to game:addScore to be one indexed instead of zero
   indexed and allow game:addScore to be used without a playerId.
3. game:renderCustomView now renders the view with top-left as the origin.
   The previous behaviour can be achieved by calling reverse(1) on the returned
   tensor.
4. Fix a bug in image.scale whereby the offset into the data was erroneously
   ignored.
5. Fix a typo in a require statement in visual_search_factory.lua.
6. Fix a few erroneous dependencies on Lua dictionary iteration order.
7. game:AddScore now works even on the final frame of an episode.

Minor Improvements:

1. Moved .map files into assets/maps/src and .bsp files into assets/maps/built.
   Added further pre-built maps, which removes the need for the expensive
   :map_assets build step.
2. Allow game to be rendered with top-left as origin instead of bottom-left.
3. Add 'mixerSeed' setting to change behaviour of all random number generators.
4. Support for BGR_INTERLEAVED and BGRD_INTERLEAVED observation formats.
5. Add a Lua API to load PNGs from file contents.
6. Add 'eyePos' to playerInfo() for a more accurate eye position of player.
   Used in place of player pos + height.
7. Add support for absl::string_view to lua::Push and lua::Read.
8. Allow player model to be overridden via 'playerModel' callback.
9. Add ability to specify custom actions via 'customDiscreteActionSpec' and
   'customDiscreteAction' callbacks.
10. Add game:console command to issue Quake 3 console commands directly.
11. Add clamp to tensor operations.
12. Add new callback api:newClientInfo, allowing each client to intercept
    when players are loading.
13. Skymaze level generation is now restricted to produce only 100000 distinct
    levels. This allows for caching to avoid expensive recompilations.
14. Add cvars 'cg_drawScriptRectanglesAlways' and 'cg_drawScriptTextAlways' to
    enable script rendering when reducedUI or minimalUI is enabled.
15. All pickup types can now choose their movement type separately, and in
    particular, all pickup types can be made static. Two separate table entries
    are now specified for an item, 'typeTag' and 'moveType'.

Deprecated Features:

1. Observation format names RGB_INTERLEAVED and RGBD_INTERLEAVED replace
   RGB_INTERLACED and RGBD_INTERLACED, respectively. The old format names
   are deprecated and will be removed in a future release.
2. The pickup item's tag member is now called moveType. The old name is
   deprecated and will be removed in a future release.