Fix irpf90_indent now does not produce white space lines

The changes can be sumarized here

• irpf90_indent now does not produce white space lines. I dont know if this should be the default behaviour, but I consider it as a good practice.
• C preprocessor macros are now never indented. This is important.
• !omp directive are now never indented. Most compilers does not care but there is definatelly one that does (a year ago I had to unindent code because of this). Also I did not add line continuation for `omp` directives. It works the same way as in fortran 90, but the new line should start with `!omp`.