.gitignore: make some ignore rules more specific to rule out side effects
.travis.yml: now that gcc is fixed, build on clang, too
LICENSE.md: there is no need for this symlink since the license file is not displayed on github anyways
README.md: This file is not in MD format, so renamed symlink to .TXT
build-mg.sh: improve configurability, script structure (will externalize distro/arch detection next)