add basher plugin

plugins/available/basher.plugin.bash

@@ -0,0 +1,14 @@
+cite about-plugin
+about-plugin 'initializes basher, the shell package manager'
+
+# https://github.com/basherpm/basher
+
+_command_exists basher ||
+  [[ -x "$HOME/.basher/bin/basher" ]] ||
+  return 0
+
+if ! _command_exists basher && [[ -x "$HOME/.basher/bin/basher" ]] ; then
+  pathmunge "$HOME/.basher/bin"
+fi
+
+eval "$(basher init - bash)"