- Added A_DamageSelf.

- A_DamageSelf(int amount, name damagetype)
- Added more A_Damage functions:

- A_DamageTarget
- A_DamageTracer
-Both take a number for how much damage to deal and the damagetype to
inflict. Negative numbers means healing.
- Added FDARI's A_JumpIf CheckClass submission.

- bool CheckClass(string classname, int ptr_select = aaptr_default, bool
match_superclass = false)
Merge branch 'checkclass' of https://github.com/MajorCooke/zdoom
Merge branch 'master' of https://github.com/Edward850/zdoom
- Fixed a possible uninitialized condition.

In the function R_RebuildViewInterpolation, the pointer 'iview' was not initialized when the player or its camera were NULL, hence 'iview == NULL' was garbage. Also, the function FindPastViewer does not return NULL, hence the mentioned check is not needed at all. Just return early if the player camera does not exist.
Merge pull request #1 from rheit/master

Merge rheit: master into MajorCooke: master
- Added FDARI's A_JumpIfHealthLower patch.

Now with pointer accessibility.
- Updated many functions.

- Added A_KillTarget(damagetype, int flags).
- Added A_KillTracer(damagetype, int flags).
- Added A_RemoveTarget.
- Added A_RemoveTracer.

A_Kill (Master/Target/Tracer/Children/Siblings):
- KILS_FOILINVUL: foils invulnerability.
- KILS_KILLMISSILES: destroys projectiles. Does not work on invulnerable
projectiles without KILS_FOILINVUL, and doesn't work at all on missiles
with NODAMAGE flag.
- KILS_NOMONSTERS: actors that are monsters will not be killed.

A_Damage (Self/Target/Master/Tracer/Children/Siblings):
- DMSS_FOILINVUL: foils invulnerability.
- DMSS_AFFECTARMOR: damages the actor's armor instead of bypassing it
entirely.
- DMSS_KILL: damages the actor by its remaining health (useful for
modular DECORATE programming).

- Added A_SpawnItemEx flags:
- SXF_SETTARGET: sets the calling actor as the target.
- SXF_SETTRACER: sets the calling actor as the tracer.
Both of these functions take priority similar to SXF_SETMASTER over
SXF_TRANSFERPOINTERS.
- consolidated the common portion of the 6 different A_Damage* functions into a subfunction.
- more redundancy removal: Consolidated the common part of the A_Kill* functions into a subfunction.
- extended parameter list of A_BFGSpray.
Merge pull request #2 from rheit/master
- Added SXF_NOPOINTERS for A_SpawnItemEx.

- Added WARPF_ABSOLUTEPOSITION for A_Warp.
- Fixed: SXF_NOPOINTERS didn't clear LastHeard, causing monsters to spawn with targets.
- removed accidentally committed .gitattributes file.