🔨 implement adverbs

[cratelyn]

this branch implements the / and \ adverbs.

for the corresponding reference pages in the J wiki, see:

• https://code.jsoftware.com/wiki/Vocabulary/slash
• https://code.jsoftware.com/wiki/Vocabulary/bslash

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✨ examples

monadic / "insert" adverb

; cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.09s
     Running `target/debug/j`
  + / 1 2 3
6

  + / 1 2 3 4
10

  * / 1 2 3
6

  * / 1 2 3 4
24

dyadic / "table" adverb

; cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.09s
     Running `target/debug/j`
  1 2 3 4 5 * / 1 2 3 4 5
1 2 3 4 5
2 4 6 8 10
3 6 9 12 15
4 8 12 16 20
5 10 15 20 25

  1 2 3 4 5 + / 1 2 3 4 5
2 3 4 5 6
3 4 5 6 7
4 5 6 7 8
5 6 7 8 9
6 7 8 9 10

monadic \ "prefix" adverb

; cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.09s
     Running `target/debug/j`
  ] \ 1 2 3
1 0 0
1 2 0
1 2 3

  ] \ 1 2 3 4 5
1 0 0 0 0
1 2 0 0 0
1 2 3 0 0
1 2 3 4 0
1 2 3 4 5

dyadic \ "infix" adverb

; cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.09s
     Running `target/debug/j`
  3 ] \ 1 2 3 4
1 2 3
2 3 4

  3 ] \ 1 2 3 4 5
1 2 3
2 3 4
3 4 5