Laravel 7 and autoload blade custom directives

[jpscharf]

• Updated for Laravel 7
• Can now autoload Balde custom directives:
  • Added an option to the config to autoload custom directives.
  • Added env variables to config.
  • Updated README.
  • Deferred StringBladeServiceProvider.
  • Added vendor/ to .gitignore.

[veneliniliev]

@TerrePorter please merge this :)

[abishekrsrikaanth]

@TerrePorter, any chance you can review this and merge.