New FlatBuffers 1.5.0 release!

[Wouter van Oortmerssen]

This is a release for those of you who prefer to not work directly from master:

https://github.com/google/flatbuffers/releases/tag/v1.5.0

A summary of what is in this release since 1.4.0:

GRPC support for Go.

C# accessors now based on structs (generates less garbage).

Improved object API (e.g. choice of pointer types, external references).

Flatc can test for conformity against older schema.

In-place binary search lookups for C# and Java.

Documentation improvements.

Many other fixes and improvements, 133 commits since 1.4.0