Report errors on standard error.
Use <ctype.h> instead of user-defined macros.
Reduce repetition in parser.
Ignore object files.
Refactor Makefile.

* Use 'CFLAGS' appropriately.

* Use implicit suffix rule for C files.

* Make 'shirka' depend on 'Makefile'.

* Remove 'shirka' executable on 'clean'.

* Make 'clean' phony.
Add path to 'could not open file' message.
Remove unnecessary 'NULL' comparisons.
Remove unnecessary casts on 'malloc' results.
Reduce nesting in conditionals.
Improve 'unknown escape sequence' message.