basic framework for command line

There's a serious bug with this, namely that it doesn't ever stop
reading stdin for input, but that can be fixed various ways. Otherwise,
in general, the command line stuff should be here in engine and look
something along these lines.
Merge remote-tracking branch 'origin/master' into command-line
basic command line threading

But it segfaults :(
added null check
added ability to add commands to the command line
merged with master
one change
commiting before merge of master
fixed merge conflicts
added more commands and fixed printing ordering
Merge branch 'command-line' of https://github.com/5-second-rule/engine into command-line
fixed a \t after one registered command
added pause command line
Merge pull request #18 from 5-second-rule/command-line

Command line merged
merge with master