Calendar overhaul

[Rekkonnect]

I'm gonna list a lot of ideas for making the calendar component better, but each can be individually accepted/rejected and prioritized.

Motivation

The calendar is a nice way to visualize a month, but it does not offer enough flexibility, like showing multiple months or restricting the month's view. It's best to avoid feature bloating but some are actually critical for a calendar, even in the CLI.

Features

• Show multiple months under the same instance
  The additional months can be laid out either vertically or horizontally, optionally with separators between them.
• Restrict the range of possible days
  • Show a specific range of days within the same month
  • Add rules to exclude specific days
  • Exclude specific days of week (for example, exclude weekends)
• Set the first day of the week
  Sometimes we want to begin the work week on Monday
• Only render specific days of week
  For example, ignore weekends and only render Mon-Fri
• Display week index
  Show the week of the month or year
• Allow picking a date within the rendered days
  • Navigate through the days with the arrow keys, highlighting the current selection with a style
  • Navigate through months with Ctrl+Arrow
    • Combinable with the rendering features described above
  • Pick a range of dates
    • Allow the user to denote the range, prompting a first selection for the start and one second selection for the end date
    • Confine the user to a range of N days, moving the selected days with the arrows

Availability

I may be able to develop some of the features, depending on the amount of effort required to pull them through.