JavaDoc tweaks

JavaDoc tweaks

Added the list of call context objects into the environment

PR changes

Bad naming in context provider options

Now with better tests and synchronisation that is more complete

Added statistics support (graphql-java#11)

* Added statistics support

* added delegating stats collector

* Added error counts to stats

* Added noop version of collector

* Made it doubles and added toMap

* javadoc warning

* batch load count is now the number of objects loaded via the batch function and batch invoke count the number of invocations of the batch function

* readme updates

* Made Statistics a class

Removing graphql dependency from dataloader

Merge pull request graphql-java#5 from graphql-java/3-instrumentation…

…-dispatcher

3 instrumentation dispatcher

Merge pull request graphql-java#5 from graphql-java/3-instrumentation…

…-dispatcher

3 instrumentation dispatcher