Better struct generation for ETH2 spec tests

[prestonvanloon]

Two tools here:

• A tool to create the nuanced structs specifically for use with Ethereum 2.0 spec tests
• Another tool to overwrite all of the hex encoded strings in the yaml and print out the new yaml.

# To generate go structs, first build the appropriate binary file
bazel build //:yaml-to-go-binary
# use that newly created binary to read your yaml file and write a new go file
dist/bin/yaml-to-go-binary path/to/data.yaml StructName
# now you have structname.yaml.go 

# To format the yaml in a proper format for encoding/json to use
bazel build //yaml-hex-to-base64
# And use that tool to print the formatted yaml, and pipe to new file
dist/bin/yaml-hex-to-base64/yaml-hex-to-base64 path/to/data.yaml > path/to/formatted.yaml