Fix schema extension handling

Bug fix release with the fix for #44 in schemagen.

Fix empty list and object results

Results for empty lists or types with no members should be included in the results. See issue #39 for more details.

Fix empty list and object results

Results for empty lists or types with no members should be included in the results. See issue #39 for more details.

Fix generated __typename resolver

I found bug #37 testing the last release against Relay. I added some asserts to one of the unit tests to protect this field in the future.

Simplify the AST handling

The change which breaks compatibility with v1.x in this release is an update to the peg::ast definition and parsing functions. It's much simpler now, with less std::unique_ptr juggling and pointer dereferencing.

Other than that, this release should be identical to v1.2.0. It brings the following changes from v1.1.0:

• GraphQL parse errors should be much easier to read now.
• Exceptions in a single field should no longer fail the entire request, instead it'll accumulate multiple errors and return them along with whatever partial results it was able to retrieve in the data member.
• Refactored the operation definition visitors to share more code and expose a public method findOperationDefinition to figure out the operation type.

Fix generated __typename resolver

I found bug #37 testing the last release against Relay. I added some asserts to one of the unit tests to protect this field in the future.

Backport error/exception handling improvements

Cherry-picking compatible fixes and features from the master branch for v1.2.0:

• GraphQL parse errors should be much easier to read now.
• Exceptions in a single field should no longer fail the entire request, instead it'll accumulate multiple errors and return them along with whatever partial results it was able to retrieve in the data member.
• Refactored the operation definition visitors to share more code and expose a public method findOperationDefinition to figure out the operation type.

Added support for matching subscription arguments

I need to make a couple of breaking API changes to fix the next set of bugs, so I'm separating the latest changes in a v1.1.x branch. The next release should be v2.0.0, unless I need to make any bug fixes in v1.x.x before then.

The new feature that bumped this up from the v1.0.x series is support for subscription arguments and filters based on those arguments. I also fixed a couple of bugs in response::Value which didn't require breaking changes to the API.

Bug fixes for enum values, interfaces, and JSON parsing

I found and fixed several bugs with a private schema I started working on that includes enum values as resolver parameters, types with multiple interface implementations, and nested JSON objects in some of the test data.

Bug fix in schemagen list value default value parsing

The same bug I fixed in v1.0.1 also exists in the schemagen list value visitor in DefaultValueVisitor.