standardize plugins, update metadata

add about-plugin metadata
chmod -x plugins
cleanup filenames to standardize on x.plugin.bash format
only plugin files intended to be executable from the command line should
contain a shebang line, and should be a+x.

plugins/available/_xterm.plugin.bash

@@ -0,0 +1,28 @@
+# This plugin is known to cause issues on OS X with the evaluation of
+# colors.  Please read [issue 108] for more information.
+#
+# You can manually turn this on by symlinking it into your
+# plugins/enabled/ directory.
+#
+# [issue 108]: https://github.com/revans/bash-it/issues/108
+
+cite about-plugin
+about-plugin 'automatically set your xterm title with host and location info'
+
+set_xterm_title () {
+    local title="$1"
+    echo -ne "\e]0;$title\007"
+}
+
+
+precmd () {
+    set_xterm_title "${USER}@${HOSTNAME} `dirs -0` $PROMPTCHAR"
+}
+
+preexec () {
+    set_xterm_title "$1 {`dirs -0`} (${USER}@${HOSTNAME})"
+}
+
+case "$TERM" in
+    xterm*|rxvt*) preexec_install;;
+esac