Background, Redirection, Parameters, and more

• Better docs 🎉
• Custom lexer and parser overhaul (see #22)
• Builtin commands started (see #24)
• New temporary REPL library and functionality
• Sources ~/.oursh_profile and can set the prompt there, e.g. export PS1="\033[32m\w\e[0m $ "
• Background processes (jobs management)
• Variables (see #51) partially implemented
• Compound commands haven't really gotten any more broken, they just never were quite right
  • e.g. background compound commands don't execute in sequence of each other
• Redirection is definitely buggy