readme, configuring eslint, changing overrides to pure react elements, easier top-level api

[bentatum]

Changes:

• Top Level API
  • { JoifulForm, JoifulInput }
• JoifulForm
  • customInputElementTypes replaced with elementTypes
  • Removed the 'Element' part of the api for this property to this elementTypes={ text, select, textarea, myCustomInput }
  • Component declaration for the elementTypes was a function, it's now a pure react component. So overriding is intuative.
• JoifulInput
  • fieldName replaced with name
  • inputProps props have been flattened
  • is is now shorthand for elementType
• Eslint