Make SQAPI object be global per module.

So functions in separate source files can call API.

TODO: Rename underlying var name?
Start module helper library.

Provides convenience API for writing modules.
Refactor to use sqmodule_helper.h helper functions.
Add popen module.

Note: name is tentative, considering adding fdopen() function and renaming
module to osstream.
Update for branch rename in squirrel-lang.
Start refactoring popen module to osstream module.
Finish refactoring popen to osstream module, add fdopen stream object.
Branch was renamed to squirrel3-genpurpose.
Update README for osstream module and other changes.
fdopen: Add unbuffered Readline() implementation.

This is grossly inefficient, but who cares when you just need it.
socket: sockaddr_in: Accept address as array.
socket: Add higher-level Socket object with stream interface.