Some fixes, per analyzers

Core/Extensions/AsChars.cs

@@ -35,4 +35,4 @@ public static Char[] AsChars(this Rune rune) {
 		/// <exception cref="InvalidOperationException">There was an issue with the internal buffers.</exception>
 		public static Char[] AsChars(this Int32 codepoint) => new Rune(codepoint).AsChars();
 	}
-}
+}

Core/Extensions/ParseInt32.cs

@@ -110,4 +110,4 @@ public static Int32 ParseInt32(this String @string, IFormatProvider provider) {
 			return Int32.Parse(@string, provider);
 		}
 	}
-}
+}

Core/Extensions/ToLower.cs

@@ -55,4 +55,4 @@ public static Rune ToLower(this Rune rune, CultureInfo culture) {
 		/// <returns>The lowercase equivalent of the <paramref name="rune"/> parameter, or the unchanged value of <paramref name="rune"/>, if <paramref name="rune"/> is already lowercase or not alphabetic.</returns>
 		public static Rune ToLowerInvariant(this Rune rune) => Rune.ToLowerInvariant(rune);
 	}
-}
+}

Core/SurrogatePair.cs

@@ -6,7 +6,7 @@ namespace Stringier {
 	/// Represents a UTF-16 Surrogate Pair.
 	/// </summary>
 	[StructLayout(LayoutKind.Auto)]
-	public readonly struct SurrogatePair {
+	public readonly struct SurrogatePair : IEquatable<SurrogatePair> {
 		/// <summary>
 		/// The high surrogate
 		/// </summary>
@@ -54,5 +54,41 @@ public SurrogatePair(CodePoint codePoint) {
 		/// Gets the <see cref="CodePoint"/> this <see cref="SurrogatePair"/> represents.
 		/// </summary>
 		public CodePoint CodePoint => new CodePoint(Unsafe.Utf16Decode(High.value, Low.value));
+
+		/// <summary>
+		/// Returns a value that indicates whether this instance is equal to a specified object.
+		/// </summary>
+		/// <param name="obj">The object to compare to.</param>
+		/// <returns><see langword="true"/> if equal to the value of this instance; otherwise, <see langword="false"/>.</returns>
+		public override Boolean Equals(Object obj) {
+			switch (obj) {
+			case SurrogatePair other:
+				return Equals(other);
+			default:
+				return false;
+			}
+		}
+
+		/// <summary>
+		/// Returns a value that indicates whether this instance is equal to a specified object.
+		/// </summary>
+		/// <param name="other">The object to compare to.</param>
+		/// <returns><see langword="true"/> if equal to the value of this instance; otherwise, <see langword="false"/>.</returns>
+		public Boolean Equals(SurrogatePair other) => High.Equals(other.High) && Low.Equals(other.Low);
+
+		/// <summary>
+		/// Returns the hash code for this instance.
+		/// </summary>
+		/// <returns>A 32-bit signed integer hash code.</returns>
+		/// <remarks>
+		/// The hash code of a <see cref="CodePoint"/> is always the integer value of the code point.
+		/// </remarks>
+		public override Int32 GetHashCode() => High.GetHashCode() ^ Low.GetHashCode();
+
+		/// <summary>
+		/// Converts the value of this instance to its equivalent string representation.
+		/// </summary>
+		/// <returns>The string representation of the value of this instance.</returns>
+		public override String ToString() => $"({High}, {Low})";
 	}
 }