add support for trapping sigabrt, sigill, sigsegv (#184)

- sigabrt: usually generated by the abort() function. Useful for cleanup prior to termination.
- sigill: issued if the user attempts to execute an illegal, malformed, or privileged instruction.
- sigsegv: issued if the user makes an invalid memory reference, such as dereferencing a null or invalid pointer.

Sources/UnixSignals/UnixSignal.swift

@@ -26,8 +26,11 @@ import Dispatch
 /// Signals are standardized messages sent to a running program to trigger specific behavior, such as quitting or error handling
 public struct UnixSignal: Hashable, Sendable, CustomStringConvertible {
     internal enum Wrapped {
+        case sigabrt
         case sighup
+        case sigill
         case sigint
+        case sigsegv
         case sigterm
         case sigusr1
         case sigusr2
@@ -49,12 +52,18 @@ public struct UnixSignal: Hashable, Sendable, CustomStringConvertible {
         return String(describing: self.wrapped)
     }
 
+    /// Usually generated by the abort() function. Useful for cleanup prior to termination.
+    public static let sigabrt = Self(.sigabrt)
     /// Hang up detected on controlling terminal or death of controlling process.
     public static let sighup = Self(.sighup)
+    /// Issued if the user attempts to execute an illegal, malformed, or privileged instruction.
+    public static let sigill = Self(.sigill)
     /// Issued if the user sends an interrupt signal.
     public static let sigint = Self(.sigint)
     /// Issued if the user sends a quit signal.
     public static let sigquit = Self(.sigquit)
+    /// Issued if the user makes an invalid memory reference, such as dereferencing a null or invalid pointer.
+    public static let sigsegv = Self(.sigsegv)
     /// Software termination signal.
     public static let sigterm = Self(.sigterm)
     public static let sigusr1 = Self(.sigusr1)
@@ -70,12 +79,18 @@ extension UnixSignal.Wrapped: Sendable {}
 extension UnixSignal.Wrapped: CustomStringConvertible {
     var description: String {
         switch self {
+        case .sigabrt:
+            return "SIGABRT"
         case .sighup:
             return "SIGHUP"
+        case .sigill:
+            return "SIGILL"
         case .sigint:
             return "SIGINT"
         case .sigquit:
             return "SIGQUIT"
+        case .sigsegv:
+            return "SIGSEGV"
         case .sigterm:
             return "SIGTERM"
         case .sigusr1:
@@ -93,12 +108,18 @@ extension UnixSignal.Wrapped: CustomStringConvertible {
 extension UnixSignal.Wrapped {
     var rawValue: Int32 {
         switch self {
+        case .sigabrt:
+            return SIGABRT
         case .sighup:
             return SIGHUP
+        case .sigill:
+            return SIGILL
         case .sigint:
             return SIGINT
         case .sigquit:
             return SIGQUIT
+        case .sigsegv:
+            return SIGSEGV
         case .sigterm:
             return SIGTERM
         case .sigusr1: