Wrapped entire code block in try to catch exceptions

Added a few different exceptions that are likely to happen
when trying to use this tool. It then offers useful feedback
and quits.

mspconvert.py

@@ -23,7 +23,8 @@ static unsigned char {0}_bits [] =
 
 outputData = b''
 
-with open(filename + ".MSP", 'rb') as f:
+try:
+    with open(filename + ".MSP", 'rb') as f:
         versionString = f.read(4)
         if versionString == b'\x4c\x69\x6e\x53':
             version = 2
@@ -92,3 +93,12 @@ with open(filename + ".MSP", 'rb') as f:
                 f.write(outputString)
                 print("Done!")
                 sys.exit(0)
+except FileNotFoundError:
+    print("{0}.MSP does not exist! Quitting...".format(filename))
+    sys.exit(255)
+except PermissionError:
+    print("Unable to open {0}.MSP -- insufficient permissions! Quitting...".format(filename))
+    sys.exit(255)
+except Exception:
+    print("Something went wrong! Quitting...")
+    sys.exit(255)