Automatically Download Flatbuffers Binaries

[gregwhitaker]

The plugin should detect the current OS and then automatically download the Flatbuffers binaries for the platform so that there is not a need to have Flatbuffers installed before running the plugin.

[shevek]

It should be possible to use https://github.com/davidmoten/flatbuffers which is a prepackaged, released version of flatc for major platforms.

Please do this?