• implement arbitrary-precision integer calculation
• implement various functions (repeat, pow10, nan, isnan, nearbyint, halt, INDEX, JOIN, IN)
• implement long options (--compact-output, --raw-output, etc.)
• implement join output options (-j, --join-output)
• implement color/monochrome output options (-C, --color-output, -M, --monochrome-output)
• refactor builtin functions