Refactor lens.c

[shaunlebron]

Nearly all the necessary features are done, so refactoring may begin to allow a better representation of its behavior for others to read and understand.

Nearly half of the code is lua specific, which should probably be separated into another file. Lua specific code should be presented through an interface of sorts, to allow plugging in different types of lens implementations, such as faster C code.

Performance is a priority in this project, and too many layers of abstraction may result in a performance hit. Must find a balance with manageability and legibility.

[shaunlebron]

This is already done.