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.

plugins/available/browser.plugin.bash

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+# based on https://gist.github.com/318247
+
+# Usage: browser
+# pipe html to a browser
+# e.g.
+# $ echo "<h1>hi mom!</h1>" | browser
+# $ ron -5 man/rip.5.ron | browser
+
+function browser() {
+    if [ -t 0 ]; then
+        if [ -n "$1" ]; then
+            open $1
+        else
+            cat <<usage
+Usage: browser
+pipe html to a browser
+
+$ echo '<h1>hi mom!</h1>' | browser
+$ ron -5 man/rip.5.ron | browser
+usage
+
+    fi
+
+    else
+        f="/tmp/browser.$RANDOM.html"
+        cat /dev/stdin > $f
+        open $f 
+    fi
+}
+
+
+# pipe hot spicy interwebs into textmate and cleanup!
+#
+# Usage: wmate
+# wget into a pipe into TextMate and force Tidy (you can undo in textmate)
+# e.g.
+# $ wmate google.com
+
+function wmate() {
+    if [ -t 0 ]; then
+        if [ -n "$1" ]; then
+            wget -qO- $1 | /usr/bin/mate
+
+TIDY=`/usr/bin/osascript << EOT
+tell application "TextMate"
+	activate
+end tell
+
+tell application "System Events"
+	tell process "TextMate"
+		tell menu bar 1
+			tell menu bar item "Bundles"
+				tell menu "Bundles"
+					tell menu item "HTML"
+						tell menu "HTML"
+							click menu item "Tidy"
+						end tell
+					end tell
+				end tell
+			end tell
+		end tell
+	end tell
+end tell
+EOT`
+
+        else
+            cat <<usage
+Usage: wmate google.com
+wget into a pipe into TextMate and force Tidy (you can undo in textmate)
+
+$ wmate google.com
+usage
+
+      fi
+    fi
+}
+
+#
+# Usage: raw google.com
+# wget into a temp file and pump it into your browser
+#
+# e.g.
+# $ raw google.com
+function raw() {
+    if [ -t 0 ]; then
+        if [ -n "$1" ]; then
+            wget -qO- $1 | browser
+        else
+            cat <<usage
+Usage: raw google.com
+wget into a temp file and pump it into your browser
+
+$ raw google.com
+usage
+      fi
+    fi
+}