2.33.0 feature release

Deprecation notices:
* --package egentoo setting is deprecated,
  --package gentoo should be used instead.
* Support for SCRIPT_DEPS and check_deps is dropped,
  REQUIREMENTS_LIST and requirements_check, introduced with ./play.it 2.31, must be used instead.
* Support for ARCHIVE global variable is dropped,
  set_current_archive, introduced with ./play.it 2.27, must be used instead.
* The following variables are no longer exposed from generated launchers:
  - APP_EXE
  - SCUMMVM_ID
* The following native libraries are no longer provided by current distributions,
  and can no longer be set as package dependencies:
  - libboost_locale.so.1.74.0
  - libminiupnpc.so.17
* The previous system for LD_PRELOAD shim support is deprecated,
  the following variables should no longer be used from game scripts:
  - PRELOAD_HACKS_LIST
  - HACK_xxx_NAME
  - HACK_xxx_DESCRIPTION
  - HACK_xxx_PACKAGE
  - HACK_xxx_SOURCE
  See "New system for LD_PRELOAD hacks" below for details.
* The following variables used to set a disk image loaded by DOSBox are deprecated:
  - GAME_IMAGE
  - GAME_IMAGE_TYPE
  See "Reworked DOSBox disk images support" below for details.
* The following functions are deprecated:
  - prefix_generate_links_farm
  - launcher_prefix_symlinks_build
  See "Launchers clean-up" below for details.

New system for LD_PRELOAD hacks:
* A new single variable LD_PRELOAD_SOURCE is exposed to game scripts,
  to set a C snippet that should be built into a .so loaded through LD_PRELOAD.

Reworked DOSBox disk images support:
* The path to a DOSBox disk image should be set with DOSBOX_DISK_IMAGE_PATH,
  a path relative to the game root.
* The type of a DOSBox disk image should be set with DOSBOX_DISK_IMAGE_TYPE,
  supported types are "iso" and "cdrom". If omitted it defaults to "iso".

Launchers clean-up:
* The launcher snippet creating a symlinks farm prefix is now printed using a single function: prefix_symlinks_generate
  This function replaces both previous functions prefix_generate_links_farm and launcher_prefix_symlinks_build.

Improved support for Adventure Game Studio games:
* An Adventure Game Studio game is identified by the AGS_NAME variable being set.
  It should be set to the ScummVM identifier, excluding the engine prefix.
* The following variables can be omitted from game scripts for Adventure Game Studio games:
  - APP_MAIN_SCUMMID
  - CONTENT_GAME_MAIN_FILES

Archive selection improvements:
* Ensure that archive_initialize_optional checks all candidates if required,
  instead of stopping at the first one with the expected name.
* Initialising an archive through archive_initialize_required / archive_initialize_optional
  sets the version string on the new archive.

Expanded context support:
* Support for contextual values (archive-specific or package-specific)
  is added for the following variables:
  - APP_xxx_DOSBOX_PRERUN
  - APP_xxx_DOSBOX_POSTRUN
  - REQUIREMENTS_LIST
  - WINE_WINEPREFIX_TWEAKS

Package properties fallback values:
* Fallback values are supported for some package properties:
  - PKG_xxx_ID
  - PKG_xxx_DESCRIPTION
  - PKG_xxx_PROVIDES
  - PKG_xxx_DEPENDENCIES_SIBLINGS
  - PKG_xxx_DEPENDENCIES_LIBRARIES
* If a value is not set for one of the following common package identifiers,
  a fallback value can used instead if it is set:
  current package         → fallback package
  PKG_BIN64 / PKG_BIN32   → PKG_BIN
  PKG_LIBS64 / PKG_LIBS32 → PKG_LIBS
  PKG_L10N_xxx            → PKG_L10N

Improvements specific to WINE games:
* Improve the ability to set custom WINEPREFIX actions from game scripts,
  by relying on a new function exposed to game scripts: wineprefix_init_custom
  By default this function does nothing, but if overridden from a game script
  its output is included in the list of actions to run on WINEPREFIX initialisation.
* A variable WINE_REGISTRY_INIT is exposed to game scripts,
  allowing to list registry keys that should be set on WINE prefix initialisation.

2.32.8

  * Fix the ability to require multiple ./play.it-provided old libraries.
  * Fix help message for --package option.
  * Add support for extra native libraries:
    - libSDL2_net-2.0.so.0
  * Add support for extra GStreamer decoders:
    - audio/x-wma
    - video/x-wmv

2.32.7

  * Restore late icons requirements check.

2.32.6

  * Allow early icons requirement check to fail for Unity3D games.

2.32.5

  * Fix support for package-specific APP_xxx_SCUMMID during launcher generation checks.
  * Fix early detection of icons for WINE and Mono games.
  * Drop late icons requirements check.
  * Prevent some ignored errors from being shown if /bin/sh = bash.
  * New package dependencies on native commands:
    - pidwait
  * New package dependencies on native libraries:
    - alleg-alsadigi.so
    - alleg-alsamidi.so
    - libaldmb.so.1
    - liballeg.so.4.4
    - libdumb.so.1