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_fuzz_test.go

@@ -73,16 +73,16 @@ func FuzzInsertLookup(f *testing.F) {
 
 				delete(expected, step.key)
 
-				_, err = actual.Get(step.key)
-				assert.Error(err)
+				_, ok := actual.Get(step.key)
+				assert.False(ok)
 			} else {
 				err := actual.Put(step.key, step.value)
 				assert.NoError(err)
 
 				expected[step.key] = step.value
 
-				found, err := actual.Get(step.key)
-				assert.NoError(err)
+				found, ok := actual.Get(step.key)
+				assert.True(ok)
 				assert.Equal(step.value, found)
 			}