Assume that every frame the player is on the ground, their pmomz will
be re-set properly if the floor is moving, therefore if the platform
STOPS, we need this to set it to 0.

This partially reverts commit a1c67e7e.

Here's how it works: When a player walks off the
moving platform, it applies their pmomz once, and
then _keeps pmomz set_ so that the camera still
adds pmomz to its movements until they hit another
floor. This way, the camera doesn't jerk around.

Also gain velocity from walking off an "up" elevator normally?

This _looks_ incorrect because the camera stops matching
the platform movement the moment you step off, but I
assure you it is a correct and accurate movement.
(Try it with chasecam off.)

Now players will apply platform movement when jumping,
but only if the platform is moving the same direction
as their jump is, and all other objects will have an
appropriate pmomz in reverse gravity FOF situations.

Closes !4.

Core code has too many #define dependencies on interface-specific
defines. This means that it's currently not possible to safely
separate the core and interface code into different contexts. The
core code should be refactored to accomadate for this because we
should not have any interface-specific code in core in the first
place.

This reverts the static library SRB2Core from a7135094 and instead
adds the core sources to the SRB2SDL2 target directly.

So frustrating...

In-source builds are pain and suffering and I am going to stop people
from doing them to save them that pain.

It still won't compile correctly. But this should avoid the error
messages related to it.

This fixes generation with USEASM enabled.

Core and SDL2 are two separate targets now. Core is a static library
that is linked into SRB2SDL2. The sources for both are separated.
When using an IDE like Visual Studio or Xcode, the source code
organized into groups that explain what that group of sources does.

In the future, "Main" could be split into a few more groups based on
file prefixes, but I think the way it is set up works for now.

Makefile targets are not affected by source_groups and typing `make`
will automatically compile both the "Core" library and SRB2SDL2
itself.

Only when actually making the debug target though!

Tested to work on MSVC, mingw-gcc

Enables ASM-NASM and adds tmap*.nas to sdl target.

No idea if this actually works.

snprintf is now available in MSVC 2015!

this is done as a POST_BUILD step

wow i'm stupid

on non debug, check assets folder in src as well

string.c, capitalization, find fixes

silently fixing a bad malloc here too shhhhhhhhh

Generates zips only at the moment

running is another story

Also support dynamic/static opengl switching