Move API description into cmd/server
Separate API from base package
Don't draw empty text
If width is passed, set height to the same as witdth

If height will be passed too, it will overwrite it anyway.
Make variables more consistent
Rename opt.Pattern -> opt.Mask
Add text rendering
Normalize in opt.FromForm directly
Rework diagonal drawing

Fix rectangles too.
Add plain pattern, set it as default
Make naming more consistent
Move image generation to image.go, extract drawDiagonal
Add pattern option, set move defaults to options.go
Add deepcopy func for opts

So that default options stay the same
Add some api documentation
Add Desc to Options, move Options to options.go