Make sure init.el is tangled before init-build, optionally allow for verbose output

[Thaodan]

• I noticed that when executing make init-build init.el isn't checked if it should be tangled first.

• Add a V=1 flag to show what commands are executed when executing make.

[tarsius]

Adding this dependency would break init-build for anyone not using init.org (i.e., most users). I've instead added a note to the documentation.

The other commit I have applied with minor modifications.