Pull request/move to lua52 module style

I've converted all the modules that don't fiddle with lua core modules
(mainly the _ext and _init suffixed modules) to the "lua 5.2" module
style.  Tested lightly by hand, and checked that the Zile test suite
still finishes without error when using my  ```next``` branch (which
is just a merge of all pending pull requests against master for integration
testing).

object.lua and parser.lua each return the single object they define, for
use like this:

```
local Object = require "object"
```

I'm not sure how to handle the various *_ext modules though.  Return
the modified table of whatever they extend (e.g. table_ext.lua ends
with ```return table```)... or perhaps more useful would be to make a
clone of the unmodified table at the start of those modules, and then
return *that* at the end, so it can be backed out programatically? In,
which case we'd load it like this:

```
local pristine_table = require "table_ext"
```