Annotate code base with JSDoc comments

[danielrearden]

The majority of the code base needs to be annotated with JSDoc comments to facilitate the generation of API documentation. This issue is intended to track the progress around this.

• graphql-tag-pluck
• load
• load-files
• loaders
• merge (partially done)
• mock
• schema (partially done)
• stitch
• wrap

I'm omitting any packages that are internal dependencies that are unlikely to be directly imported by anyone consuming graphql-tools, but if you think any of the omitted packages should also be documented, let me know and I can amend the list. Additional tasks relating to this process:

• Add @deprecated tag where appropriate (for example anything relating to the legacy directive implementations)
• Add @internal to any functions or types unlikely to be consumed directly to reduce the noise in the generated docs as much as possible
• Remove the API references at the bottom of the existing documentation pages (if this is done at all, it should only be done once the generated docs are up to snuff)

[yaacovCR]

Totally in favor myself :) time is an issue :(