Todo

• Subshell
  • Backtick subshell
  • Dollar sign subshell
• Pipelines
  • better pipelines that don't require EOF
• Basic single quote strings
• Double quote strings with substitutions
• Environment handling
  • Calling variables
  • Assigning Variables
  • Return values with $?
• Control Flow
  • if
  • elif
  • else
  • while
  • for
• Lists
  • And-if (||)
  • Or-if (&&)
• Background process control
• Alias
• essential built-ins
  • list of posix built ins at the bottom
  • cd
  • exit
  • true/false