execline - script language to rely entirely on chain loading

execline is the first script language to rely entirely on chain loading. An execline script is a single argv, made of a chain of programs designed to perform their action then exec() into the next one.
The execlineb command is a launcher: it reads and parses a text file, converting it to an argv, then executes into that argv. It does nothing more.
Straightforward scripts like nice -10 echo blah will be run just as they are, without the shell overhead. Here is what the script could look like:
```
#!/command/execlineb -P
nice -10
echo blah
```
More complex scripts will include calls to other execline commands, which are meant to provide some control over the process state and execution flow from inside an argv.