mmap instead of fopen

Use mmap instead of fopen in parse_file in order to gain ~15-20% performance
when parsing a file.
Document ngp to make Erwan happy :)
Ignore return value (-Werror) because handling the
error is the same as the nominal case

Also update Makefile.am since README.md was moved to
README for autotools
Fix 2 bugs from colorize and mmap

- In colorize there was no check on the strstr which could lead to
segfaults
- In mmap we didn't always close the file in error cases which could
  lead to errno 24
isfile is really a boolean but I don't use C99 boolean so make it int
Change color numbers by an enum for readability

yay, a legitimate enum use !
Remove libconfig dependency

It was really a pain because it's not a default on any system.
Plus the changes were trivial enough to justify a simple removal.