Makefile cleanup

- do not generate MANIFEST file, rely on automatic generation;
- clean properly, spec file was not rebuilt after clean.
Avoid buffer overflow reading character glyphs

font_data is used as an index into a 256 array so make sure is always in
range 0-255.
Avoid to use iaddr if NULL.

Although quite not probable this could happen.
Handle file descriptor as as valid.

Although unlikely to return 0 (as already used) creat function could
return 0 as a file descriptor. Handle 0 as success instead of failure.
Fix small memory leak

If fopen fails k was not freed.
Remove useless check

rest cannot be NULL here.
Add help option

Allow to have some help without having to look at the code.
Fix some command line handling

- fix some typos in --help option;
- return error if wrong arguments used.