Make flow types available by including source file in NPM release.

[nmn]

If the build system is updated to to just copy all the source files with the .js.flow extension next to the built files, flow will pick up the type definitions.

Further, this is the best way to provide flow type definitions as there is no need to maintain a separate type definition file and changes in the source code will automatically show for users using the library.

(Will try to do a PR)

[iamchenxin]

@nmn I made a solution (flow-dynamic ) to deal with graphql's Flow Type conflict with another packages . See #359 ,seems leebyron worried about Static Type conflict between packages before. Many of us are hoping a .js.flow in official graphql package.

[aweary]

@nmn will this change expose internal flow type definitions? For example, if I wanted to import the Document type from graphql/language/ast?

[nmn]

@aweary If any type is exported from its file (using export type) it will be made available.

Further all values imported from module will come with their associated types.

[leebyron]

Merging into #359