Add AL_EXT_BFORMAT to alext.h
Use a wave file channel mask based on the actual format
Invert the ChannelOffsets array
Combine some fields into a struct
Show prettier names in the alsoft-config sample format combo boxes
Use better GUI item names for the resampler option
Use an ambisonics-based panning method

For mono sources, third-order ambisonics is utilized to generate panning gains.
The general idea is that a panned mono sound can be encoded into b-format
ambisonics as:

w[i] = sample[i] * 0.7071;
x[i] = sample[i] * dir[0];
y[i] = sample[i] * dir[1];
...

and subsequently rendered using:

output[chan][i] = w[i] * w_coeffs[chan] +
                  x[i] * x_coeffs[chan] +
                  y[i] * y_coeffs[chan] +
                  ...;

By reordering the math, channel gains can be generated by doing:

gain[chan] = 0.7071 * w_coeffs[chan] +
             dir[0] * x_coeffs[chan] +
             dir[1] * y_coeffs[chan] +
             ...;

which then get applied as normal:

output[chan][i] = sample[i] * gain[chan];

One of the reasons to use ambisonics for panning is that it provides arguably
better reproduction for sounds emanating from between two speakers. As well,
this makes it easier to pan in all 3 dimensions, with for instance a "3D7.1" or
8-channel cube speaker configuration by simply providing the necessary
coefficients (this will need some work since some methods still use angle-based
panpot, particularly multi-channel sources).

Unfortunately, the math to reliably generate the coefficients for a given
speaker configuration is too costly to do at run-time. They have to be pre-
generated based on a pre-specified speaker arangement, which means the config
options for tweaking speaker angles are no longer supportable. Eventually I
hope to provide config options for custom coefficients, which can either be
generated and written in manually, or via alsoft-config from user-specified
speaker positions.

The current default set of coefficients were generated using the MATLAB scripts
(compatible with GNU Octave) from the excellent Ambisonic Decoder Toolbox, at
https://bitbucket.org/ambidecodertoolbox/adt/
Use size_t for the vector size and capacity
Copy the null terminator from the string instead of appending it
Add a cast for MSVC
Use VECTOR_FIND_IF instead of manual loops
Use helpers to set the gain step values
Don't use ComputeAngleGains for SetGains
Make ComputeAngleGains use ComputeDirectionalGains
Store default speaker configurations in a struct
Add a helper to search for a channel index by name
Fix stereo device configuration
Avoid taking the square-root of the ambient gain

Although it is more correct for preserving the apparent volume, the ambisonics-
based panning does not work on the same power scale, making it louder by
comparison.
Make alcSuspendContext and alcProcessContext batch updates

This behavior better matches Creative's hardware drivers and Rapture3D's OpenAL
driver. A compatibility environment variable is provided to restore the old
no-op behavior for any app that behaves badly from this change (set
__ALSOFT_SUSPEND_CONTEXT to "ignore").

If too many apps have a problem with this, the default behavior may need to be
changed to ignore, with the env var providing an option to defer/batch instead.
Don't attempt to match a channel input to output

I don't like this, but it's currently necessary. The problem is that the
ambisonics-based panning does not maintain consistent energy output, which
causes sounds mapped directly to an output channel to be louder compared to
when being panned. The inconcistent energy output is partly by design, as it's
trying to render a full 3D sound field and at least attempts to correct for
imbalanced speaker layouts.