Fix README; clean up C code
Switch from MIT to BSD 3-clause license
Update for Lua 5.2; add information fields

The module has been updated to use the 5.2 API rather than the 5.1 one. Lua
5.1 is no longer supported.

In addition, I've added the following information fields to the module's
exported table:

+ _VERSION
+ _AUTHOR
+ _URL
+ _LICENSE

The content of these will be pretty obvious. I owe the idea to @kikito.