Create the concept of enabled plugins

This allows users to disable a plugin without completely removing it.
Instead, they simply remove the `plugins/enabled/*.bash` file for the
plugin they want to disable.  This continues the concept of "everything
on" while providing greater flexibility to future users.

It might be a good idea to allow turning these off by default in the
future and allowing not only the `plugins/enabled/*.bash` files but also
an array of `<plugin_name>` values that would search for
`plugins/available/<plugin_name>.plugin.bash` to enable them.  That
method would make it easier for people custom tune their plugins from
within their `.bash_profile` script.

bash_it.sh

@@ -25,7 +25,7 @@ do
 done
 
 # Plugins
-PLUGINS="${BASH}/plugins/*.bash"
+PLUGINS="${BASH}/plugins/enabled/*.bash"
 for config_file in $PLUGINS
 do
   source $config_file

plugins/enabled/base.plugin.bash

@@ -0,0 +1 @@
+../available/base.plugin.bash

plugins/enabled/battery.plugin.bash

@@ -0,0 +1 @@
+../available/battery.plugin.bash

plugins/enabled/browser.plugin.bash

@@ -0,0 +1 @@
+../available/browser.plugin.bash

plugins/enabled/dirs.plugins.bash

@@ -0,0 +1 @@
+../available/dirs.plugins.bash

plugins/enabled/git.plugins.bash

@@ -0,0 +1 @@
+../available/git.plugins.bash

plugins/enabled/hg.plugins.bash

@@ -0,0 +1 @@
+../available/hg.plugins.bash

plugins/enabled/javascript.plugins.bash

@@ -0,0 +1 @@
+../available/javascript.plugins.bash

plugins/enabled/jekyll.plugins.bash

@@ -0,0 +1 @@
+../available/jekyll.plugins.bash

plugins/enabled/latex.plugin.bash

@@ -0,0 +1 @@
+../available/latex.plugin.bash

plugins/enabled/nginx.plugins.bash

@@ -0,0 +1 @@
+../available/nginx.plugins.bash

plugins/enabled/osx.plugin.bash

@@ -0,0 +1 @@
+../available/osx.plugin.bash

plugins/enabled/python.plugin.bash

@@ -0,0 +1 @@
+../available/python.plugin.bash

plugins/enabled/ruby.plugin.bash

@@ -0,0 +1 @@
+../available/ruby.plugin.bash

plugins/enabled/rvm.plugin.bash

@@ -0,0 +1 @@
+../available/rvm.plugin.bash

plugins/enabled/ssh.plugins.bash

@@ -0,0 +1 @@
+../available/ssh.plugins.bash

plugins/enabled/subversion.plugin.bash

@@ -0,0 +1 @@
+../available/subversion.plugin.bash

plugins/enabled/tmux.plugin.bash

@@ -0,0 +1 @@
+../available/tmux.plugin.bash

plugins/enabled/vagrant.plugins.bash

@@ -0,0 +1 @@
+../available/vagrant.plugins.bash

plugins/enabled/virtualenv.plugin.bash

@@ -0,0 +1 @@
+../available/virtualenv.plugin.bash

plugins/enabled/z.bash

@@ -0,0 +1 @@
+../available/z.bash