luamin flag to preserve property names
luamin renames not only names of variables but also names of properties of objects stored in variables referenced with dot syntax: `var.prop` might become `a.b`. In Lua, it is also possible to refer to a property with indexing syntax, where the property name is a runtime expression: `var["prop"]`, or even `var["pr" + x]`. When a PICO-8 cart uses both dot syntax and indexing syntax to refer to the same property, when luamin renames the dot syntax is breaks the runtime indexing. There's no way to programmatically transform the indexing code to work with the new name.

It is rare (and, IMO, poor style) for Lua code to use both dot syntax and indexing syntax for the same property, but it can be useful in some PICO-8 applications. Carts that use this technique need property renaming disabled, at least for the specific properties referred to both ways. luamin could just never rename properties to solve for this edge case, but at the significant expense of carts that only refer to a property with dot syntax: `var.some_long_prop_name` becomes `a.some_long_prop_name`.

The next best thing would be to allow the user to disable property renaming with a flag to the tool: `p8tool luamin --no-rename-properties foo.p8` (This was proposed in [PR 54](https://github.com/dansanderson/picotool/pull/54/files) as a `luamin2` variation, though it works better as a flag.) This might be the most practical solution.

A refinement might be to allow the user to provide a list of property name patterns to preserve (because the indexing technique is most useful for property names that conform to a pattern), either as an external file or with tool hints in the source itself: `-- @proppattern elem\d+` would preserve `x.elem1`, `abc.elem987`, etc. and allow for `x["elem" + n]`.

It is provably impossible to detect when indexing a variable would refer to a specific property in all cases. Consider: `x.prop = 1; y = x; y.prop = 2` Or: `x.prop = 1; y.obj = x; z = "obj"; y[z]["prop"] = 2` It may be possible to detect some simpler cases, such as indexing only used with constant expressions. I doubt this would be worth the effort for PICO-8 applications.