CLI

[electricjesus]

(Ignore the commits spam.. it will be rebased later)

On this PR:

• Added build, parse, and lex CLI via spf13/cobra
• Also updated README.md
• Added dependency management
• Heavily modified Makefile

TODOs:

• functional CLI testing, wrapping tests that were implemented via cmd-crossplane branch

NEXT (future features, not necessary to this MVP PR):

• Add persistent settings (via spf13/viper) for long flags
• Ensure errors should be errors and should be available via stderr, no need to be flag-controlled
• we'll change the format subcommand behaviour to take in stdin and output stdout just like go fmt so we could use it as a formatter for various IDEs