read VERSION > manpage, fix MANDIR, set mode for executable just to be sure

This is a suggestion how we could generate the manpage dynamically. It works without any template files, but moves the gzipman step to make install. I oriented myself on dwm's Makefile. Additionally the manpage now install to the correct directory. 
I also took the freedom to include two minor (imo) improvements:
- make install now compiles the binaries if not already done
- make install now explicitly sets the mode for the executable

Let me know what you think.

(For the future: should I put all those changes in one single commit or rather split it into several? In this case it would be 4 commits: One for the version stuff, the second for the MANDIR, the third for make install: all and the last one for the executable mode.)