refactor!: shorter constructors, bucket → subtable (#22)

## Description

Currently, the name of `bucket` is a bit confusing, because it is considered a 'table' in literature (as well as the whole hash table). A `bucket` is better described as a 'subtable', which is used by the total hash table to perform cuckoo hashing.

In addition, the constructors `NewTable`, `NewTableBy`, and `NewCustomTable` were given shorter names, because the package name `cuckoo` already implies that `New*` would create a hash table with cuckoo hashing. This package has one use-case, and so it unambiguous what constructors produce.

## Changes

- `NewTable` -> `New`
- `NewTableBy` -> `NewBy`
- `NewCustomTable` -> `NewCustom`
- `bucket` -> `subtable`

### Design Decisions

- I would have renamed `Table` and `subtable` to map equivalents, but 'submap' implies that a certain subsection of the map is contained within it, which isn't quite right.
- I chose not to go with `Map` and `table`, because of the split naming convention.

## Checklist

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

Reviewed-on: #22
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>

settings.go

@@ -9,7 +9,7 @@ import "fmt"
 const DefaultCapacity uint64 = 16
 
 // DefaultGrowthFactor is the standard resize multiplier for a [Table]. Most
-// hash table implementations use 2.
+// implementations use 2.
 const DefaultGrowthFactor uint64 = 2
 
 // defaultMinimumLoad is the default lowest acceptable occupancy of a [Table].
@@ -26,10 +26,10 @@ type settings struct {
 }
 
 // An Option modifies the settings of a [Table]. It is used in its constructors
-// like [NewTable], for example.
+// like [New], for example.
 type Option func(*settings)
 
-// Capacity modifies the starting capacity of each bucket of the [Table]. The
+// Capacity modifies the starting capacity of each subtable of the [Table]. The
 // value must be non-negative.
 func Capacity(value int) Option {
 	if value < 0 {