Fix rendering gaps on polys with upper/lower textures

See merge request STJr/SRB2!453

Disable the APNG code if the version of libpng is greater than 1.4.

See merge request STJr/SRB2!457

Since supposedly the current code *can't* work with newer versions of libpng that have the apng patch, it won't compile if that's what people have.
It seems like some distros are adding the apng patch to libpng and that'll make things annoying to compile for people.
I think it goes without saying, but if there's ever a fix to make newer libpng versions work with the APNG code then this can be reverted.

Resolve buffer overflow crash when configuring System Menu and GIF controls

See merge request STJr/SRB2!445

Update capslock state on window re-focus

See merge request STJr/SRB2!436

Make AppVeyor installer paths consistent with Travis installer paths

See merge request STJr/SRB2!446

Make AppVeyor installer paths consistent with Travis installer paths(assets/deployer/installer -> assets/installer)

MinGW64:Target nocona for 64-bit builds [revision]

See merge request STJr/SRB2!440

Add 64-bit job to Appveyor

See merge request STJr/SRB2!442

Add Windows installer building to AppVeyor

See merge request STJr/SRB2!443

ARM and ARM64 support with MSVC toolchain

See merge request STJr/SRB2!412

Update code versions to 2.1.23

See merge request STJr/SRB2!435

Hide SRB2-CHAT behind #ifndef NONET

See merge request STJr/SRB2!434

Fix saving game progress on a unmodified game

See merge request STJr/SRB2!433

Fix -ANGLE_180 because MSVC complains

See merge request STJr/SRB2!432

-ANGLE_180 evaluates equal to ANGLE_180.