Support various OpenAL Soft extensions

[icculus]

There are several extensions from OpenAL Soft that are totally reasonable to support. Go through the list at that link and see what we can plug in here trivially.

[icculus]

Things we can probably handle:

• AL_EXT_32bit_formats ... just int32 mono/stereo. It lists others if you support AL_EXT_MCFORMATS too.
• AL_EXT_source_distance_model
• AL_EXT_thread_local_context
• AL_SOFT_buffer_sub_data
• AL_SOFT_direct_channels
• AL_SOFT_direct_channels_remix
• AL_SOFT_gain_clamp_ex
• ALC_SOFT_output_mode
• ALC_SOFT_pause_device

Things we can maybe handle:

• AL_EXT_debug
• AL_EXT_direct_context. LOTS of entry points and related extensions...but most of it can probably happen with macro magic and light refactoring.
• AL_SOFT_buffer_samples
• AL_SOFT_callback_buffer
• AL_SOFT_deferred_updates.txt
• AL_SOFT_events
• AL_SOFT_loop_points
• ALC_SOFT_reopen_device
• AL_SOFT_source_length
• AL_SOFT_source_spatialize

Might be doable, but could be painful:

• ALC_SOFT_loopback
• ALC_SOFT_system_events

Things we likely can't handle, or would take a lot of work, needs external dependencies or complex data formats, needs things SDL doesn't provide, or would simply be difficult to do reasonably in a single-file OpenAL implementation:

• AL_SOFT_HRTF
• AL_SOFT_MSADPCM
• AL_SOFT_UHJ
• AL_SOFT_UHJ_ex
• AL_SOFT_bformat_ex
• AL_SOFT_bformat_hoa
• AL_SOFT_block_alignment
• AL_SOFT_buffer_length_query (doable but not really useful without some of these other extensions.)
• AL_SOFT_device_clock
• AL_SOFT_effect_target
• ALC_SOFT_loopback_bformat
• ALC_SOFT_output_limiter
• ALC_SOFT_source_latency
• AL_SOFT_source_resampler
• AL_SOFT_source_start_delay

[leiradel]

+1 to AL_SOFT_callback_buffer, as it allows user code to correctly synchronize real-time audio and video.