Closes #6: Bundler support added

plugins/bundler/bi.fish

+function bi
+  bundle install $argv
+end

plugins/bundler/bu.fish

+function bu
+  bundle update $argv
+end

plugins/bundler/bundler.load.fish

+# The following is based on https://github.com/gma/bundler-exec
+
+## Functions
+function _bundler-installed
+  which bundle >- ^&1
+end
+
+function _within-bundled-project
+  set -l check_dir $PWD
+  while [ $check_dir != "/" ]
+    [ -f "$check_dir/Gemfile" ] and return
+    set check_dir (dirname $check_dir)
+  end
+  false
+end
+
+function _run-with-bundler
+  if _bundler-installed and _within-bundled-project
+    command bundle exec $argv
+  else
+    $argv
+  end
+end
+
+### Main program
+set -l bundled_commands annotate cap capify cucumber foreman guard middleman nanoc rackup rainbows rake rspec ruby shotgun spec spinach spork thin thor unicorn unicorn_rails
+
+for cmd in $bundled_commands
+  if not contains $cmd bundle gem
+    eval "function $cmd; _run-with-bundler $cmd \$argv; end"
+  end
+end