Cleanup Makefile.

Stopped using non-standard rm(1) flags: While these worked on some
distribtions, being non-standard, they simply fail on others, and we can work
around them anyway.
Noticably, this fixes installation on BSDs and other non-GNU *nix
distributions.

Use install(1) instead of cp(1) and mkdir(1), since it's cleaner (ie: easier to
read), shorter and makes sure permissions are what we want the to be is
standard in makefiles.
Merge pull request #21 from hobarrera/make

Cleanup Makefile.