Instead just use nullptr to represent no thread is active.

Thread: Correctly set main thread initial stack position

Implement I4 texture format

@neobrain, could you confirm that this is correct?

It's been tested with various different games and fixes different textures, including in Animal Crossing, Kirby Triple Deluxe, and SMB3D.

Fix crashes due to un-initialized GSP shared memory

Give each emulated thread it's own TLS memory

The TLS area for thread T with id Ti is located at TLS_AREA_VADDR + (Ti - 1) * 0x200.
This allows some games like Mario Kart 7 to continue further.

This works around crashes related to GSP/HID/etc. shared memory blocks
having garbage values. The proper fix requires proper management of
mapped memory blocks in the process.

GPU improvements

nihstro: Update submodule to latest upstream/master to support MADI instruction decoding.

Common: Remove the BIT macro

When the macro was introduced in 326ec512
it wasn't noticed that it conflicted in name with a heavily used macro
inside of dyncom. This causes some compiler warnings. Since it's only
lightly used, it was opted to simply remove the new macro.

Small memory map definitions cleanup

Also adds better documentation and removes the one-off reimplementation
of the function in pica.h.

Loader: Remove .bin file support

It is of very limited practical utility currently, and will soon be
impossible to support due to more accurate memory map emulation.

Kernel: Process class and ExHeader caps parsing

This has been obsoleted by the field in Process.