First version of the SOurce SDK 2013
Fixed various missing files
Adding a CONTRIBUTING file so the rights that GitHub users grant to Valve with Contributions are clearly outlined.
Add executable permission to ccache and protoc.
Mac: Fix corrupted protoc binaries.

These binaries were corrupted due to accidental newline ending conversion.
Add executable bit to gendbg.sh.
Rename GameInfo.txt to gameinfo.txt
Merge pull request #49 from ntgd/master

Fix 'gameinfo.txt' doesn't exist in subdirectory 'source-sdk-2013/mp/game/mod_hl2mp/'
Check in gitattributes for binaries.

Followup to @TheSeg's comments on 5f08baa.
* Switched the SDK from checked-in projects to VPC, the Valve Project Creator. See the Getting Started document on the wiki for details.
* Pulled in bug fixes from HL2 and HL2MP.
Fixed execute permissions on OSX/Linux scripts and binaries.
Merge https://github.com/ValveSoftware/source-sdk-2013
Updated the libs. Updated vpc_* to include support for $Conditional in .vgc files. Included vstdlib_exclude.vpc for the OSX builds.
Update text & binary attributes.

This should prevent line ending issues.
Normalize line endings

Fixes issue #75.
Added some more files to .gitignore. Added technical guidelines for pull requests to CONTRIBUTING
Merge https://github.com/ValveSoftware/source-sdk-2013