Handle mapped program memory segment aliasing properly, on WCH RISC-V targets

- Added `program_segment_key` target config param, to allow the user to specify the desired program memory segment
- Added the ability to resolve the currently aliased segment, by means of probing the mapped segment
- Added program counter transformation, when the mapped segment is aliasing a foreign segment
- Other bites of tidying

src/Targets/RiscV/Exceptions/IllegalMemoryAccess.hpp

@@ -0,0 +1,18 @@
+#pragma once
+
+#include "src/TargetController/Exceptions/TargetOperationFailure.hpp"
+
+namespace Exceptions
+{
+    class IllegalMemoryAccess: public TargetOperationFailure
+    {
+    public:
+        explicit IllegalMemoryAccess()
+            : TargetOperationFailure("Illegal memory access")
+        {}
+
+        explicit IllegalMemoryAccess(const std::string& message)
+            : TargetOperationFailure(message)
+        {}
+    };
+}