MAKE: standardize install variables
MAKE: standardize install variables

- convert to autotools-like variables commonly used in build scripts
- respect DESTDIR (used for temporary install locations)
- fix symlink logic to work with DESTDIR
${foo##bar} is posix, see:
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html
under "2.6.2 Parameter Expansion"
- quote all variables that can contain whitespace
(make does not take care of that!)

pedrosnk/elixir,gfvcastro/elixir,lexmag/elixir,lexmag/elixir,michalmuskala/elixir,beedub/elixir,kimshrier/elixir,elixir-lang/elixir,ggcampinho/elixir,gfvcastro/elixir,joshprice/elixir,kimshrier/elixir,antipax/elixir,ggcampinho/elixir,beedub/elixir,antipax/elixir,kelvinst/elixir,kelvinst/elixir,pedrosnk/elixir