added singularity install script

[rzuw273]

No description provided.

[greatfireball]

Please do a rebase on the master branch, due to some changes have been performed there, e.g. removal of pullapprove integreation.

Second and more important, I would consider to perform the installation via a package which should be easier to remove than the make/make install installation. Instructions how to generate and install a debian package are provided here. Moreover, please use an official release from github instead of the master/development branche with the exception if you need up-to-date features which are not yet included in an official release. Currently, I would suggest the release v2.2.1 as suggested by the official installation guide.

For the compilation you need to install some dependencies, see last paragraph of the section Build a RPM from source: sudo apt-get install -y build-essential libtool autotools-dev automake autoconf

Please add that dependency installation also to your script, to ensure, that it can be run independently.

One huge plus would be an test script, if singularity is installed and runs correctly. Therefore, I would suggest a separate folder t/ containing all test scripts which can be linked to the individual test folders inside the installation subfolders. @iimog already implemented some test here using bats. For a single installation script, like yours, testing of an existing singularity and its functionality should be enough.