Include the filename in the error messages

TODO

@@ -7,14 +7,13 @@
 - Move constants to the symbol table, so we can check at parse time for duplicates.
 - Don't pass raw pointers to the visitor methods.
 - While loop.
-- Comparision operators.
+- Type checking.
 - Procedures.
 - Calculate additional stack space needed for subexpressions in the allocator
   visitor and not in the backend.
 - Support immediates greater than 12 bits.
 - It seems instructions are correctly encoded only if the compiler is running
   on a little endian architecture.
-- Print filename in the error message.
 - Merge declaration and definition nodes.
 
 # Shell
@@ -33,4 +32,3 @@
 ## Appearance
 
 - Add a bar with additional information under the prompt (edit_bar), like the hostname.
-- Show current time in the prompt.