setup_linux.sh: make the distro available to external scripts

Discovering the Linux distribution and parsing the arguments must always
be done as the first steps. Checking the permissions must come later.
Otherwise it wouldn't even be possible to do a `./setup_linux.sh -h`.
setup_linux.sh: fix invalid syntax error, assigning true to variable
setup_development_tools.sh: for now, only install vim

When a new software is added, it will have its own function, it will have
to be explicitly added to the main.
setup_linux.sh: make USERS variable from external scripts

This way, if a tool installation needs to change user's config files, it
will know what users want these modifications.
setup_linux.sh: development tools must be installed as a last step

It doesn't matter if this is performed before or after the system update,
but it can't be run when parsing the arguments.

Without this commit the command `./setup_linux.sh --devel --users foo`
would try to run `setup_linux.sh` first, which wouldn't even have the
users variable set.

Therefore, from now on, all the optional choices retrieved from the
arguments and run the appropriate ones only in the final steps.
setup_development_options.sh: set up vim config file for all users
Rename setup_development_options.sh to setup_devel_tools.sh
These commits contain a series of fixes and additions.

Now, setup_linux nstalls vim when the --devel option is specified and adds a
very basic configuration file for development.

The users are exported in the variable USERS so that an external script added
by anyone doesn't have to bother about that.