* Ignore files in .prettierignore

Fixes #88

* Force the babylon parser when parsing not-js files

Forcing the parser stops errors that are caused by trying to run a JS
fragment through the graphql / markdown parsers.

The 'html' parser has not yet been released yet, but will be in Prettier
1.15.

This uses a block list over an allow list because I expect the list of
"file types with a prettier parser that could contain javascript fragments"
will grow at a slower pace than "file types with a prettier parser that
are variations of the javascript language".

Fixes #98, Fixes #81

Run the format script and commit updates

Ensure we test with eslint 3.x, 4.x and 5.x, and node 10

Fixes #97

Node v4, v7 and v9 are end of life and no longer supported.

This lets us remove some conditional checks for some APIs that we now
know will be present.

This shall also allow us to drop pragma support as people can use the
native pragma suppport in prettier (to be done in a later commit).

Prettier now provides native pragma support using @Format or @prettier
notation. Use that instead of our implementation

Fixes #48, Fixes #54

These were used in the release script, but that's been abstracted away
now

ESLint v5.0.0 is the minimum supported version

Drop support for specifying prettier options using the "fb" shorthand
string. Replace "fb" with either config in your .prettierrc or the object:
`{ singleQuote: true, trailingComma: 'all', bracketSpacing: false, jsxBracketSameLine: true, parser: 'flow'}`

Drop support for specifying the prettier options as `null`. Replace
`null` with an empty object `{}`

Move these two functions into a helper module 'prettier-linter-helpers'.
If you used those functions then plese reference that package directly.

Fixes #101

This was removed in a prior version because other linting tools ended up
depending on helper functions within eslint-plugin-prettier and did not
want to inadvertently install eslint as a transitive dependency. Now that
those helpers have been extracted into a separate package those other
linting tools should depend upon that instead of eslint-plugin-prettier.