install.sh: Script to set up a development environment

Script that sets up the development environment of my liking on all OSs
I use (OS X, Fedora, Ubuntu).

Installs packages, Python modules and Vim plugins, and deploys the
config config files from the script's directory.

Collects the following pieces of information:
- Package names from 'packages' (by platform);
- Python module names from 'pip-modules';
- Config file locations from the config files themselves;
- Vim plug-in clone URLs from vimrc.

Prerequisites on OS X: Xcode and MacPorts already installed.
vimrc: Mac-specific key mappings

Remapping keys of my full size UK-layout Apple keyboard.
- Remap '§' key to Escape.
- Swap '£' and '#' keys. It's more convenient than changing the keyboard
  layout to US because I use '£' in other applications.
install.sh: Generate SSH keys

Generates a public RSA key and stores in '~/.ssh/id_rsa.pub'.