Astrophot

Minor update to improve the way models and parameters print. Includes more helpful information in a readable format. Also updates to some spelling/grammar in the docs.

Total rewrite of the parameter system. Now a full directed acyclic graph with generality for a variety of constraint types. The new system represents each parameter as a node in a graph, it is possible to link nodes to achieve a variety of goals. The main purposes of such a system are to allow:

- Any two parameters may be given an equality constraint by having one simply point to the other in the graph.
- A spatially varying PSF can be achieved by creating parameters that define the spatial variation and then having the PSF parameters point to them through a function
- SED constraints are possible by similarly having brightness parameters point to some functional form of the SED.
- An astrometry correction for multi-image analysis can be created by adding a shift to the position of all objects in a single image.

A lot of creativity is possible with these constraints. A new tutorial is provided to give the basic ideas. Please contact us if you want to try something new with these capabilities!

Major update to coordinate systems for AstroPhot. Now explicit mappings for world (celestial sphere), tangent plane, and pixel coordinates. This makes it far easier to automatically align multiple images, or to use catalogues of objects with RA/DEC coordinates. It is now possible for these cases to map between each other quickly and easily.

Major rework was done for `Window` objects, they now handle a great deal of information to map between all coordinate systems. Some of the functionality that was in `Image_header` is moved to them.

A new `WCS` class is created to deal with abstract coordinate transforms.

A new page in the docs is added to explain the details of all the coordinate transformations and possible mistakes that can be made.

Big thanks to wmwv for identifying this limitation and helping make the updates work smoothly!

Starting to build out more complete docs!

More substantial docs have been added for:
- Target_Image
- AstroPhot_Model
- LM
- utils

This includes some mathematical expressions to aid the explanations. More will come and please send requests if there are features you would like better explanations for!

Also updated is the naming for AstroPhot models. If a name is not provided then AstroPhot will just automatically generate a unique name instead of throwing an error. This makes it more convenient to create a large number of models if you don't care about the names.

`Target_Image` has been updated so that it can take a weight matrix instead of a variance. Sometimes this is more desirable as a bad pixel can be given a weight of 0, which is more computationally stable than giving a variance of infinity.

Minor bug fix. WCS from astropy provides pixel scale matrix in deg, AstroPhot was assuming arcsec. This is now fixed so most images can be loaded with WCS and should be automatically aligned.

An example of this was added in the getting started notebook. The JointModelling notebook now makes use of the WCS to align the images from various bands.

Rename everything to `AstroPhot` due to name conflict with another code.