Remove globals, etc.

[airstruck]

• Removes all globals (main ROT module, and some hoisted functions).
• Introduces a base class, ROT.Class, so that all classes are declared in a uniform way.
• User can drop in a different class library by overwriting ROT.Class before requiring the main library. The new base class just needs to be given an extend function conforming to 30log's API.
• 30log is made optional; a minimal shim is provided as a fallback. The shim provides all 30log features currently used by rotLove and nothing else.

Also updated preciseWithMovingPlayer demo just for testing purposes (none of the demos tested the files in /src; they weren't actually working due to a few typos).

[airstruck]

Just tried swapping 30log out with Middleclass; looks something like this:

local class = require 'middleclass'
BaseClass = class('BaseClass')

function BaseClass:initialize (...)
    self:init(...)
end

function BaseClass:extend (name, proto)
    local child = class(name, self)
    if proto then
        for k, v in pairs(proto) do child[k] = v end
    end
    return child
end

Could be useful if someone wants a particular class library badly enough, maybe for serialization or debugging.