Add CS_DMG_HEADSHOT define

but i don't know if it works in other games.

( I'm using this already in my only headshot plugin - https://forums.alliedmods.net/showthread.php?t=234169 and works fine in CSS/CSGO )
Fix version script failing when HEAD directly contains hash instead of ref to it.
Add Travis-CI config file.
Give define value (of 1) to PLATFORM defs to match the same-name defs in some SDKs.
Merge pull request #8 from psychonic/travis-ci

Add support for Travis-CI
Merge pull request #10 from psychonic/platform-defs

Fix up PLATFORM defs to match same-name ones in some SDK versions.
Quell isNaN MSVC performance warning.
Fix build.
Merge pull request #9 from KyleSanderson/amtlutilloudness

Quell isNaN MSVC performance warning.
Move many player natives from core to logic.
Merge pull request #12 from psychonic/more2logic

Move many player natives from core to logic.
Update CS:GO Gamedata
Move adminsys and more natives from core to logic.
Replace magic numbers for sm_show_activity with named constants.
Merge pull request #13 from psychonic/adminsys2logic

Move adminsys and more natives from core to logic (r=asherkin).
Merge pull request #14 from psychonic/rip-magic

Replace magic numbers for sm_show_activity with named constants (r=asherkin).
Fix Mac build.
Really fix Mac build.
Merge pull request #7 from Bara20/patch-1

Add CS_DMG_HEADSHOT define (r=psychonic).
Create CONTRIBUTING.md

As discussed in #11.