Remove context export (#515)

* Added link to hooks-based error component example

* doctoc readme

* Removed context export

src/index.js

@@ -2,7 +2,6 @@
 export { default as Field } from './Field'
 export { default as Form, version } from './ReactFinalForm'
 export { default as FormSpy } from './FormSpy'
-export { default as ReactFinalFormContext } from './context'
 export { default as useField } from './useField'
 export { default as useFormState } from './useFormState'
 export { default as useForm } from './useForm'