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/ssh.plugin.bash

@@ -0,0 +1,19 @@
+cite about-plugin
+about-plugin 'ssh helper functions'
+
+function add_ssh() {
+  about 'add entry to ssh config'
+  param '1: host'
+  param '2: hostname'
+  param '3: user'
+  group 'ssh'
+
+  echo -en "\n\nHost $1\n  HostName $2\n  User $3\n  ServerAliveInterval 30\n  ServerAliveCountMax 120" >> ~/.ssh/config
+}
+
+function sshlist() {
+  about 'list hosts defined in ssh config'
+  group 'ssh'
+
+  awk '$1 ~ /Host$/ { print $2 }' ~/.ssh/config
+}