Add base configuration

- Follow XDG standard: ~/.config and ~/.local folders
- Set environment variables and define aliases within ~/.config/shell
- Add installation script for easy setup and maintenance
  (i.e., `dotfiles-install` and `dotfiles-update`)
- Add README.md with info on the installation and general notes

.config/shell/aliases

@@ -0,0 +1,55 @@
+#!/bin/sh
+
+# Aliases used in all kinds of shells
+
+
+# Manage the bare `git` repository in ~/ holding the dotfiles
+alias dotfiles='git --git-dir=$DOTFILES_DIR --work-tree=$HOME'
+
+
+
+alias path='echo $PATH | tr ":" "\n"'
+
+
+# Easier `cd` movements
+alias ..='cd ..'
+alias ...='cd ../..'
+alias ....='cd ../../..'
+alias .....='cd ../../../..'
+
+
+# Use human-readable sizes
+alias df='df --human-readable'
+alias du='du --human-readable'
+alias free='free --human'
+
+
+# Make the terminal more colorful
+
+alias diff='diff --color=auto'
+alias grep='grep --color=auto --exclude-dir=.git'
+alias ip='ip -color=auto'
+
+if _command_exists dircolors; then
+
+    # Compute `$LS_COLORS` only once because this file is also sourced
+    # by every non-interactive `bash` via `$BASH_ENV` (e.g., ":!cmd" in `vi`)
+    if [ -z "${LS_COLORS:-}" ]; then
+        if [ -r "$XDG_CONFIG_HOME/dircolors" ]; then
+            eval "$(dircolors -b "$XDG_CONFIG_HOME/dircolors")"
+        else
+            eval "$(dircolors -b)"
+        fi
+    fi
+
+    alias ls='ls --color=auto'
+
+fi
+
+
+# Add common `ls` utilities
+alias l='ls --classify --format=vertical'
+alias la='ls --classify --format=vertical --almost-all'
+alias lal='ls --classify --format=long --almost-all'
+alias ll='ls --classify --format=long'
+alias lla='lal'