Add dev versions
Remove gcc-multilib
Merge remote-tracking branch 'upstream/master'
Update build versions

sourcemod 1.4 is long gone and 1.7 is being worked on currently.
Because 1.7 is in active development it is marked to allow failed
builds.
Merge pull request #2 from CrimsonTautology/master

Remove version 1.4;  add versions 1.6 and 1.7