Add pictorial elements

[cdelker]

With the addition of ElementImage in 51bf481, users may import graphical elements such as Arduinos, Raspberry Pis, etc. This opens the possibility of adding "Pictorial" schematic elements in the style of Fritzing, where the Element is a picture rather than the traditional schematic symbol, often seen on sites like Adafruit and Sparkfun. Consider adding a pictorial module to schemdraw, with:

1. A core library of often-used pictorial components such as a breadboard, resistor, capacitor, diode, LED
2. Ability to parse Fritzing files, such that images like the ones published by Adafruit may be loaded in as elements.

Note: There doesn't seem to be a straightforward way to place an SVG in a Matplotlib axis without requiring something like cairosvg and rasterizing it first. Could limit such an interface to schemdraw's SVG backend only.

[cdelker]

Version 0.19