New Installation Procedure

# Overview
Updated installation procedure. User is not advised anymore to add an `alias` to his `~/.bashrc`, but to run an installation script.

# Details

## Defaults and Customized Install Directories
Per default the installation script (`install.sh`) installs into `~/bin`, in order to allow the user to run the command w/o needing sudo privileges.
Call:
`./install.sh`

If the user wants to install `lpp` and `pizza` somewhere else, he can specify the respective prefix.
Call:
`./install.sh -p path/to/install/dir`

## Procedure

The script
- asserts that the install directory exists
- asserts that no old installations are present
- creates symbolic links
- updates the `PATH` variable in `~/.bashrc`, if `lpp` cannot be found after the installation