Lua version of runCommand

`dfhack.internal.runCommand(command)`: Returns a table of `{color, text}` tables and command result as `status`.
`dfhack.run_command(command)`: Runs a command (similar to run_script) and returns its output as a string along with its exit code
Usage (`print` prints its first argument):
```
[lua]# ~(dfhack.run_command('print "a b"'))
a b
[lua]# ~(dfhack.run_command('print', 'a b'))
a b
[lua]# ~(dfhack.run_command({'print', 'a b'}))
a b
[lua]# ~(dfhack.run_command('print', {'a b'}))
a b
[lua]# ~(dfhack.run_command('print', {'a', 'b'}))
a
```