Make pro icon installation steps clearer

It can be a little bit confusing when you say this "directory". it looks like "lib/fonts" directory. I had a little trouble until I figured it out :/

Fixes #84 by exporting icon_data.dart

This allows dynamic loading of icons based on their code point without the use of maps.

Also adds simple documentation to icon_data.dart

update font awesome to 5.13

Include Font awesome attribution in license

Change suggestion on how to depend on pro icons

Solves version solving fails

Attribution [similar to their own](https://github.com/FortAwesome/Font-Awesome/blob/master/css/all.css#L2-L3). Separated from the main license according to [LicenseRegistry](https://api.flutter.dev/flutter/foundation/LicenseRegistry-class.html). Not quite sure what to do if a user loads pro icons - we could remove the last line (link to free license) in the generator script - but I'm not sure if that wouldn't be overkill

Move non-public files to src, Add duotone support, Fix #76

Add FaIcon Widget to fix alignment / cutoff issues for folks

Version 8.6.0

  - Update to Font Awesome 5.12.1
  - Move to Flutter Community
  - Instructions for Supporting pro icons

Add support for pro icons, fix #45

Provide update script for Windows

Update font awesome to 5.12

Fix #52

This allows users to update the icons on Windows computers as well. Requires at least Windows 7. The update mechanic works the same as in update.sh, but with the tweaks of #37 to recognize a custom icons.json (https://github.com/brianegan/font_awesome_flutter/pull/37/commits/dd08ea2e5ff2812fe5a5569d33936ce14a518c15) already in there.

Fix #52 by indicaticating that the project's example is a flutter project and provide a link to view it

updated to font awesome 5.9

- This step is necessary since the `IconDataLight` block is now commented out by default to avoid unnecessary classes when pro icons are not installed.
- Also added myself to the contributors list - sneaky me

feat(README): add info for build refresh

The link would lead to michaelspiss/font_awesome_flutter, which will no longer exist once the pull request is merged.
Sadly, github does not provide a way to create relative links to the archive.