Update tmux status with named constants for colors

Changes to tmux.conf
- Make it easier for users to adjust the colorscheme by using named
  constants to store the color names.
- Highlight the active window using additional attributes instead of
  a jarring background.
- Enable the aggressive-resize option
- Remove unused key bindings
- Bind L to choose-session
- Allow the escape key to quit the choice window

tmux.conf

@@ -13,6 +13,9 @@ set-option -sg escape-time 50
 # Enable UTF-8
 set-window-option -g utf8 on
 
+# Don't constrain the window size to smallest client size
+set-window-option -g aggressive-resize on
+
 # Enable mouse mode
 set-option -g mode-mouse on
 set-option -g mouse-select-pane on
@@ -37,18 +40,25 @@ set-option -g display-time 1500
 set-option -g base-index 1
 set-option -g pane-base-index 1
 
+# Configure the tmux colours
+# Based on Solarized [altercation/solarized] on GitHub
+TMUX_STATUS_BG=brightblack
+TMUX_STATUS_FG=white
+TMUX_MESSAGE_BG=brightblack
+TMUX_MESSAGE_FG=brightred
+
 # Status bar
 set-option -g status on
 set-option -g status-interval 2
-set-option -g status-bg colour8
-set-option -g status-fg colour7
+set-option -g status-bg $TMUX_STATUS_BG
+set-option -g status-fg $TMUX_STATUS_FG
 set-option -g status-utf8 on
 
 # Status bar - left
 # <username>@<host> <session name>
 set-option -g  status-left "#[fg=blue]#(whoami) "
 set-option -ga status-left "#[fg=green]#h "
-set-option -ga status-left "#[default][#S]"
+set-option -ga status-left "#[fg=brightmagenta][#S]"
 # Status bar - left length
 set-option -g status-left-length 40
 
@@ -60,18 +70,19 @@ set-option -ga status-right "#[fg=red]#(~/bin/stardate)"
 set-option -g status-right-length 30
 
 # Status bar - window status
-set-window-option -g window-status-current-bg red
-set-window-option -g window-status-current-fg colour7
-set-window-option -g window-status-bg colour8
-set-window-option -g window-status-fg colour7
-set-window-option -g window-status-format "#I-#P:#W#F"
-set-window-option -g window-status-current-format "#I-#P:#W#F"
+set-window-option -g window-status-current-bg $TMUX_STATUS_BG
+set-window-option -g window-status-current-fg cyan
+set-window-option -g window-status-current-attr underscore
+set-window-option -g window-status-bg $TMUX_STATUS_BG
+set-window-option -g window-status-fg $TMUX_STATUS_FG
+set-window-option -g window-status-format "#I.#P:#W#F"
+set-window-option -g window-status-current-format "#I.#P:#W#F"
 
 # Message bar formatting
-set-option -g message-bg colour7
-set-option -g message-fg black
-set-option -g message-command-bg black
-set-option -g message-command-fg colour7
+set-option -g message-bg $TMUX_MESSAGE_BG
+set-option -g message-fg $TMUX_MESSAGE_FG
+set-option -g message-command-bg $TMUX_MESSAGE_FG
+set-option -g message-command-fg $TMUX_MESSAGE_BG
 
 # Pane highlighting
 set-option -g pane-active-border-fg green
@@ -136,6 +147,21 @@ bind-key - \
 # screen and the scrollback buffer too
 bind-key -n C-k clear-history
 
+# Disable the choose-client key binding. It usually results in the current
+# client getting detached.
+unbind-key D
+
+# Rather than go with the last session, let the user pick from the list
+# of available sessions
+bind-key L choose-session
+
+# Don't waste time with the next-window and previous-window bindings
+unbind-key n
+unbind-key p
+
+# Allow the escape key to quit the choice window
+bind-key -t vi-choice Escape cancel
+
 # Terminator style pane switching
 # OSX Terminal.app, enable Use option as meta key
 # and delete the key bindings for Option Cursor left & Option Cursor right