🐛 Correctly parse RC PHP version (#132)

It'll be a while before a new release candidate is available, but this
bug has now been resolved.

A new `PhpVersionNumber.parse` method has been added which can throw.

The `VersionExtractor` class is now capable of extracting version
numbers from all strings now too, and isn't just used to determine
the Valet version number.

New tests have been added to handle these scenarios.

This commit also removes the phpmon-cli component, which wasn't being
updated or maintained (it was an experiment).

phpmon-tests/PhpVersionNumberTest.swift

@@ -11,6 +11,10 @@ import XCTest
 class PhpVersionNumberTest: XCTestCase {
 
     func testCanDeconstructPhpVersion() throws {
+        XCTAssertEqual(
+            try! PhpVersionNumber.parse("PHP 8.1.0RC5-dev"),
+            PhpVersionNumber(major: 8, minor: 1, patch: 0)
+        )
         XCTAssertEqual(
             PhpVersionNumber.make(from: "8.0.11"),
             PhpVersionNumber(major: 8, minor: 0, patch: 11)
@@ -29,6 +33,12 @@ class PhpVersionNumberTest: XCTestCase {
         )
     }
     
+    func testPhpVersionNumberParse() throws {
+        XCTAssertThrowsError(try PhpVersionNumber.parse("OOF")) { error in
+            XCTAssertTrue(error is VersionParseError)
+        }
+    }
+    
     func testCanCheckFixedConstraints() throws {
         XCTAssertEqual(
             PhpVersionNumberCollection