feat!: update get from (V, error) to (V, bool) (#20)

## Description

Currently, the signature for `Table.Get` is `func (K) (V, error)`. This is not very Go-idiomatic, which prefers to return a boolean instead of an error. For instance, a built-in Go map is used like so:

```go
if value, ok := users[id]; !ok {
  // ...
}
```

Updating our table to look like that is best practice. In that same vein, to support direct lookup (i.e. `v := users[id]`), this PR also adds `Table.Find`.

## Changes

- BREAKING CHANGE: Update contract of `Table.Get` to `func (K) (V, bool)`. Returns 'false' is the item cannot be found, and 'true' if it is found.
- Add `Table.Find`.
- Updated tests and documentation to match the change.

### Design Decisions

- Chose to make this decision because throwing an error implies that there is something 'wrong' with the table. There is nothing wrong with the table; it is just that the item does not exist.

## Checklist

- [x] Tests pass
- [x] Docs updated

Reviewed-on: #20
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>

cuckoo_test.go

@@ -108,12 +108,12 @@ func TestGetMany(t *testing.T) {
 	}
 
 	for i := range 2_000 {
-		value, err := table.Get(i)
+		value, ok := table.Get(i)
 		if i < 1_000 {
-			assert.NoError(err)
+			assert.True(ok)
 			assert.Equal(value, true)
 		} else {
-			assert.Error(err)
+			assert.False(ok)
 		}
 	}
 }