Implement FILEMAN:Copy(string fromPath, string toPath)

Copies a file from `fromPath` to `toPath`. Returns `true` if the file
was copied successfully.

Docs/Luadoc/Lua.xml

@@ -1592,6 +1592,7 @@
 			<Function name='destroy'/>
 		</Class>
 		<Class name='RageFileManager'>
+			<Function name='Copy'/>
 			<Function name='DoesFileExist'/>
 			<Function name='GetDirListing'/>
 			<Function name='GetFileSizeBytes'/>