Set up basic project structure

Main module is in the folder aperturesynth.

Tests go in aperturesynth/tests.

Docs go in doc.
Refactor registerstack into logically separate modules

Separate responsibilities more clearly for each of the distinct
elements in the program.

Core modules:
- register, provides a class for matching to a specific image
- synthesise, for combining registered images
- gui, for providing necessary interface details
- io, for handling loading and saving files
Refactor aperture_synthesis into sensible modules

Reorganise the major functions into distinct modules:
register - for handling the matching of images
synthesise - for handling the load/synthesise/save components
gui - stub for handling future interface components