* rename files, render_file -> file_main, render_node -> node_main, mandelbrot -> render_mandelbrot
* make the error message stuff in common a /lot/ neater (a single function and a set of macros)
* clean up rest of code to use those new macros

committer: Tero Marttila <terom@fixme.fi>

.*.swp
*.o
render_file
render_node
web_main
*.png