ucaptcha: Generate CAPTCHA validation with custom effects

This class can generate CAPTCHA validation with custom effects.

It can generate an image with random characters from a configurable list of allowed characters sets.

The text can be obfuscated with several types of noise effects like grayscale noise, color noise, dots, lines, circles, polygons, grind, chessboard, random characters, cartesian, polar and parametric function plot, background image, logo watermark.

The class can also several types of effects randomly to the image like warp, wave, shear, breeze, rotate and convolution.

The generated image is return as a string in the PNG format.