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

.profile

@@ -0,0 +1,83 @@
+#!/bin/sh
+
+# Main setup file executed for all kinds of shells
+
+
+# Prevent loading ~/.profile twice in `bash`
+export PROFILE_LOADED=1
+
+
+# Basic utilities
+
+_command_exists() {
+    command -v "$1" 1>/dev/null 2>&1
+}
+
+_in_bash() {
+    [ -n "$BASH_VERSION" ]
+}
+
+_in_zsh() {
+    [ -n "$ZSH_VERSION" ]
+}
+
+_prepend_to_path () {
+    if [ -d "$1" ] ; then        # Ignore non-existing directories
+        case :$PATH: in
+            *:"$1":*) ;;         # Already in the `$PATH` => Do nothing
+            *) PATH=$1:$PATH ;;  # Otherwise, prepend it
+        esac
+    fi
+}
+
+_remove_from_path () {
+    _rest=$PATH                         # Not yet processed `$PATH`s
+    _new=                               # `$PATH`s collected so far
+
+    while [ -n "$_rest" ]; do           # Rebuild the `$PATH` entry by entry
+
+        _dir=${_rest%%:*}               # First remaining entry
+
+        case $_rest in
+            *:*) _rest=${_rest#*:} ;;   # Drop that entry and its colon
+              *) _rest= ;;              # Last entry read => Stop
+        esac
+
+        [ "$_dir" = "$1" ] && continue  # Skip on an exact match
+
+        _new=${_new:+$_new:}$_dir       # Append, avoiding a leading colon
+
+    done
+
+    PATH=$_new
+
+    unset _dir _new _rest
+}
+
+
+_remove_from_path "/usr/games"
+_remove_from_path "/usr/local/games"
+
+_prepend_to_path "$HOME/.local/bin"
+
+
+# Needs ~/.local/bin on the `$PATH` already
+# because it checks existence of some binaries
+[ -f "$HOME/.config/shell/env" ] && . "$HOME/.config/shell/env"
+
+
+[ -f "$HOME/.config/shell/aliases" ] && . "$HOME/.config/shell/aliases"
+
+
+# Source ~/.profile_local, which holds machine-specific ENV variables
+[ -f "$HOME/.profile_local" ] && . "$HOME/.profile_local"
+
+
+# Load `bash`-specific configurations
+if [ -n "$BASH_VERSION" ] && [ -f "$HOME/.bashrc" ]; then
+    . "$HOME/.bashrc"
+fi
+
+
+# Ensure ~/.profile is loaded each time `bash` starts
+unset PROFILE_LOADED