Add Help command to open help in a new command

help-argument-taking syntax taken from [Opening vim help in a vertical split window](http://stackoverflow.com/a/14601793/578288)
Stop airline from checking for trailing whitespace

Because it gave me too many false positives for whitespace I wanted
Make TrailingWhitespaceDelete use a function that sets useful options

The documentation for using “&” to read or set an option is “expr-option”.
Update DetectIndent plugin
Wrap autocommands in augroups to avoid slowdowns

Recommended by http://learnvimscriptthehardway.stevelosh.com/chapters/14.html

I also added an indent setting for Clojure, to match the comment. Checking for filetype `lisp` worked before when I was detecting Clojure myself, but now Clojure has a filetype of its own because I installed vim-polyglot.