add flatbuffers

commit 6da1cf79d90eb242e7da5318241d42279a3df3ba
Author: Max Burke <max@urbanlogiq.com>
Date:   Sun Jan 19 14:47:28 2020 -0800

    [rust] Add use declarations to Rust-generated bindings for imported FB definitions (#5645)

    * Bugfix for Rust generation of union fields named with language keywords

flatbuffers/docs/source/SwiftUsage.md

@@ -0,0 +1,93 @@
+Use in Swift {#flatbuffers_guide_use_swift}
+=========
+
+## Before you get started
+
+Before diving into the FlatBuffers usage in Swift, it should be noted that
+the [Tutorial](@ref flatbuffers_guide_tutorial) page has a complete guide
+to general FlatBuffers usage in all of the supported languages (including Swift).
+This page is designed to cover the nuances of FlatBuffers usage, specific to
+Swift.
+
+You should also have read the [Building](@ref flatbuffers_guide_building)
+documentation to build `flatc` and should be familiar with
+[Using the schema compiler](@ref flatbuffers_guide_using_schema_compiler) and
+[Writing a schema](@ref flatbuffers_guide_writing_schema).
+
+## FlatBuffers Swift library code location
+
+The code for the FlatBuffers Swift library can be found at
+`flatbuffers/swift`. You can browse the library code on the [FlatBuffers
+GitHub page](https://github.com/google/flatbuffers/tree/master/swift).
+
+## Testing the FlatBuffers Swift library
+
+The code to test the Swift library can be found at `flatbuffers/Flatbuffers.Test.Swift`.
+The test code itself is located in [Flatbuffers.Test.Swift](https://github.com/google/
+flatbuffers/blob/master/tests/FlatBuffers.Test.Swift).
+
+To run the tests, use the [SwiftTest.sh](https://github.com/google/flatbuffers/
+blob/master/tests/FlatBuffers.Test.Swift/SwiftTest.sh) shell script.
+
+*Note: The shell script requires [Swift](https://swift.org) to
+be installed.*
+
+## Using the FlatBuffers Swift library
+
+*Note: See [Tutorial](@ref flatbuffers_guide_tutorial) for a more in-depth
+example of how to use FlatBuffers in Swift.*
+
+FlatBuffers supports reading and writing binary FlatBuffers in Swift.
+
+To use FlatBuffers in your own code, first generate Swift structs from your
+schema with the `--swift` option to `flatc`. Then include FlatBuffers using `SPM` in
+by adding the path to `FlatBuffers/swift` into it. The generated code should also be
+added to xcode or the path of the package you will be using. Note: sometimes xcode cant
+and wont see the generated files, so it's better that you copy them to xcode.
+
+For example, here is how you would read a FlatBuffer binary file in Swift: First,
+include the library and copy thegenerated code. Then read a FlatBuffer binary file or
+a data object from the server, which you can pass into the `GetRootAsMonster` function.
+
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.swift}
+    import FlatBuffers
+
+    typealias Monster1 = MyGame.Sample.Monster
+    typealias Vec3 = MyGame.Sample.Vec3
+
+    let path = FileManager.default.currentDirectoryPath
+    let url = URL(fileURLWithPath: path, isDirectory: true).appendingPathComponent("monsterdata_test").appendingPathExtension("mon")
+    guard let data = try? Data(contentsOf: url) else { return }
+
+    let monster = Monster.getRootAsMonster(bb: ByteBuffer(data: data))
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Now you can access values like this:
+
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.swift}
+    let hp = monster.hp
+    let pos = monster.pos
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+In some cases it's necessary to modify values in an existing FlatBuffer in place (without creating a copy). For this reason, scalar fields of a Flatbuffer table or struct can be mutated.
+
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.swift}
+    let monster = Monster.getRootAsMonster(bb: ByteBuffer(data: data))
+
+    if !monster.mutate(hp: 10) {
+      fatalError("couldn't mutate")
+    }
+    // mutate a struct field
+    let vec = monster.pos.mutate(z: 4)
+
+    // This mutation will fail because the mana field is not available in
+    // the buffer. It should be set when creating the buffer.
+    if !monster.mutate(mana: 20) {
+      fatalError("couldn't mutate")
+    }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The term `mutate` is used instead of `set` to indicate that this is a special use case. All mutate functions return a boolean value which is false if the field we're trying to mutate is not available in the buffer.
+
+<br>