ASCII art to Unicode converter

Small CLI program to convert ASCII box drawings to unicode. Inspired by svgbob and The Monads Hidden Behind Every Zipper.

> aa2u
+-------------+             |
| Hello World |             |  -----+
+-------------+             |       |     +--+
                            |       +-----+  |
----------------------------+                |
                            |         +------+
          +-----+---.       |         |
          |     +---+       |   +--+  |
      .---|         |---.   |   |  |  |
      |   +---------+   |#  |   |  |  |
      |                 |#  |   |  +--+
      '-----------------'#  |   +---------+
        ##################  |

+------+-----+---------+
| This | is  | a table |
+------+-----+---------+
| It   | has | some    |
+------+-----+---------+
| values     |         |
+------+-----+---------+
| 0    | 1   | 2  | 3  |
+------+-----+----+----+
^D
┌─────────────┐             │
│ Hello World │             │  ─────┐
└─────────────┘             │       │     ┌──┐
                            │       └─────┘  │
────────────────────────────┤                │
                            │         ┌──────┘
          ┌─────┬───╮       │         │
          │     └───┤       │   ┌──┐  │
      ╭───│         │───╮   │   │  │  │
      │   └─────────┘   │█  │   │  │  │
      │                 │█  │   │  └──┘
      ╰─────────────────╯█  │   └──────────
        ██████████████████  │

┌──────┬─────┬─────────┐
│ This │ is  │ a table │
├──────┼─────┼─────────┤
│ It   │ has │ some    │
├──────┴─────┼─────────┤
│ values     │         │
├──────┬─────┼─────────┤
│ 0    │ 1   │ 2  │ 3  │
└──────┴─────┴────┴────┘

Usage:

aa2u > outfile  # Reads from stdin
aa2u < infile   # Prints to stdout
aa2u infile     # Input file as argument works as well
aa2u < infile > outfile  # Convert a file