Issue #4: Added From trait (#7)

* #4 Added `From` trait

This adds the `from()` and `tryFrom()` methods to pure enums, and the `fromName()` and `tryFromName()` methods for all enum types.

* Code review changes

Dropped support for fragile indexes on pure enums

* Dropped unnecessary array_pop()

* import ValueError

* remove import

Co-authored-by: Samuel Štancl <samuel@archte.ch>
Co-authored-by: Samuel Štancl <samuel.stancl@gmail.com>

README.md

@@ -6,6 +6,7 @@ A collection of enum helpers for PHP.
 - [`Names`](#names)
 - [`Values`](#values)
 - [`Options`](#options)
+- [`From`](#from)
 
 You can read more about the idea on [Twitter](https://twitter.com/archtechx/status/1495158228757270528). I originally wanted to include the `InvokableCases` helper in [`archtechx/helpers`](https://github.com/archtechx/helpers), but it makes more sense to make it a separate dependency and use it *inside* the other package.
 
@@ -186,6 +187,65 @@ TaskStatus::options(); // ['INCOMPLETE' => 0, 'COMPLETED' => 1, 'CANCELED' => 2]
 Role::options(); // ['ADMINISTRATOR', 'SUBSCRIBER', 'GUEST']
 ```
 
+### From
+
+This helper adds `from()` and `tryFrom()` to pure enums, and adds `fromName()` and `tryFromName()` to all enums.
+
+#### Important Notes:
+* `BackedEnum` instances already implement their own `from()` and `tryFrom()` methods, which will not be overridden by this trait. Attempting to override those methods in a `BackedEnum` causes a fatal error.
+* Pure enums only have named cases and not values, so the `from()` and `tryFrom()` methods are functionally equivalent to `fromName()` and `tryFromName()`
+
+#### Apply the trait on your enum
+```php
+use ArchTech\Enums\From;
+
+enum TaskStatus: int
+{
+    use From;
+
+    case INCOMPLETE = 0;
+    case COMPLETED = 1;
+    case CANCELED = 2;
+}
+
+enum Role
+{
+    use From;
+    
+    case ADMINISTRATOR;
+    case SUBSCRIBER;
+    case GUEST;
+}
+```
+
+#### Use the `from()` method
+```php
+Role::from('ADMINISTRATOR'); // Role::ADMINISTRATOR
+Role::from('NOBODY'); // Error: ValueError
+```
+
+#### Use the `tryFrom()` method
+```php
+Role::tryFrom('GUEST'); // Role::GUEST
+Role::tryFrom('NEVER'); // null
+```
+
+#### Use the `fromName()` method
+```php
+TaskStatus::fromName('INCOMPLETE'); // TaskStatus::INCOMPLETE
+TaskStatus::fromName('MISSING'); // Error: ValueError
+Role::fromName('SUBSCRIBER'); // Role::SUBSCRIBER
+Role::fromName('HACKER'); // Error: ValueError
+```
+
+#### Use the `tryFromName()` method
+```php
+TaskStatus::tryFromName('COMPLETED'); // TaskStatus::COMPLETED
+TaskStatus::tryFromName('NOTHING'); // null
+Role::tryFromName('GUEST'); // Role::GUEST
+Role::tryFromName('TESTER'); // null
+```
+
 ## Development
 
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